It's hard to hone in on the essence of stealth. Many stealth games focus on slow, methodical movement and punish you for slipping up, but others give you the opportunity to react before your cover's blown, or abandon the idea of caution altogether. Which of these truly defines stealth?

We believe the truth is somewhere in the foggy middle. The common denominator that links these games is knowing how, when, and where to stay hidden, but the specifics are not explicit. At the same time, good stealth games also give you little guidance and happily kick you into the fray to let you figure things out for yourself. The true measure of a stealth game, then, is freedom: the freedom to explore what stealth means, while giving you a place to plot, learn, and screw up for yourself. With that standard set, we've smoked out the 15 best stealth games of all time to show you what this shadowy genre is made of. Don't look away though, or they might escape.

The original Sly Cooper did something few mascot games ever manage - it was a genuinely great genre game, with a cast of universally loveable characters. Sly 2 is basically Sly+, with a raft of improvements and expansions on the stealth formula. But with all the same anthropomorphic heroes. Good.

The stealth is so tight and feature packed, and laid the foundations for the stick-to-the-city free-running of inFamous. Sly’s sneaking is more traditional, while support characters like Bentley and Murray mix it up with more gadget-heavy / combat-heavy stealth, respectively. The result is a well rounded sneaking game with a charming cast and absolutely loads of stuff to do. And it isn’t all dark and gritty like most…

Stealth Inc is the suspiciously bright passageway where stealth mechanics and mini-games meet. In a series of time trials, you - a sphere-headed clone with giant glowing eyes - must solve all the puzzles in a given room before the aggressive machines inside spot and kill you. You're unarmed and will die the instant they hone in on your position, so all you have are your wits and shadows to keep you alive. And it works remarkably well.

Gleefully tossing aside the gritty environment, gadgetry, and slow movement common to most stealth games, Stealth Inc goes for something more colorful and frantic, where you're encouraged to speed through the level as fast as you can without getting killed. Yet the stealth mechanics are absolutely essential for the game to function, and the controls for movement are incredibly tight, so it's no one's fault but your own if you stumble into a puddle of light and get vaporized. It's the ultimate test of a very different kind of stealth, where speed is favored over caution.

Second Sight, Free Radical’s unjustly forgotten original leaves you painfully vulnerable from the start. Controlling the sickly John Vattic, you wake up wearing nothing but hospital scrubs with no clue where you are, how you got there, or much about who you even are. The amnesiac patient may not be the most original protagonist, but he’s certainly one that immediately makes you want to hide until you know what the hell is going on. What makes Vattic’s stealthy hunt for safety so pleasurable is that he can control people and objects with his brain.

Like a cross between Solid Snake and a particularly wan Ben Kenobi, the most fun you have as Vattic is figuring out which of your freaky psychic abilities is best suited to getting you out of a jam. Does it make sense to possess a guard and shoot all the others? Use an astral projection to scout ahead and determine the best path around them? Vattic’s arsenal of skills, coupled with a story jumping in time, proved Free Radical can make more than just an excellent shooter.

When Rocksteady rebranded Batman’s sneak punching as ‘Predator Mode’, it wasn’t screwing about. Arkham City's approach to combative hide-and-seek is one of total domination, of giving you the tools and the information to concoct emergent, creative, horrifyingly powerful divide-and-conquer strategies on the fly. Rather than concerning you with claustrophobic creep-and-dodge work over your immediate vicinity, Arkham’s approach is to give you vantage and control over the whole arena: its every gantry and walkway, its every intricate path, route, and flow of activity.

Except when it’s not. It balances that sense of dominion, with an immediate fragility should things go wrong. Lose your concentration, slip up, fail to spot something important, and you’ll be panicked and flapping away in fright in an instant. That’s the dichotomy that makes Arkham’s stealth so good. It’s about cleverly making you look unstoppable, while knowing that you’re anything but. In short, it’s about being Batman.

Is Riddick strictly a stealth game? Probably not. It’s a mix of sneaky-sneaky, stabby-stabby, and punchy-punchy. But that’s no bad thing - the way stealth and more brutal combat mix makes for a pleasing, bloody adventure. As the perpetually on-the-run Riddick, it’s your job to escape Butcher… look, it’s all in the game name. You do so by fighting your way out of the cells, then getting into the vent system, and eventually off the planet.

It’s the executions that really make this game, combined with the savage first-person combat when things inevitably require a bit of brute force. Oh, and those fancy night-vision specs that Riddick uses are a neat way of avoiding the trap many stealth games fall into, where you end up staring at the screen for hours because everything's so damn dark.

The best games take complex concepts and make performing them feel effortless, and Gunpoint's low-fi take on the stealth genre is one of the best. Don't be fooled by its simplicity, though - its pixelated graphics and sidescrolling gameplay belie one of the smartest, funniest stealth puzzle games ever made.

Armed with a special hacking device called the Crosslink, a pair of hydraulic 'hypertrousers,' your fists and your own wits, you must infiltrate each of Gunpoint's expertly crafted levels without being detected. Your special pants let you blast up the side of buildings, attach to ceilings, and launch into guards to provide a few swift punches to their face. And your Crosslink allows you to hack into nearly anything (like light switches and security cameras) and rewire them to open doors or activate enemy weapons. It's one thing to completely ghost a level - it's another entirely to reprogram everything inside the level and manipulate the guards to solve it for you. Gunpoint may not offer as many weapons, camo patterns, or other fun stealth gadgets as other games on this list, but its simplicity proves that less is indeed more.

While similar in many ways to the Hitman games that came before, Blood Money improves on an already strong stealth system with a setup that rewards perfectly silent missions, and makes life a whole lot harder when you don't pull it off.

While the goal of any stealth game is to get from whatever window you crawled through to a certain goal without being seen, the threat of discovery usually ends when you finish the mission. Not so in Blood Money, where 47's notoriety rises every time he's spotted by a guard or security camera, and that notoriety makes him more recognizable to enemies in the missions that follow. You have to be on the ball at all times, and Blood Money gives you all the tools to make that happen, from elaborate costumes to new mechanics that make it much easier to dispose of a body or knock out the lights to a whole building. Everything in Blood Money has a place and a use, and the only limit on how well they work is your own skill.

Good stealth games give you a wide variety of tools and options to help you out of a jam if you get spotted; great ones encourage you to never want to go loud in the first place. While later entries in the Splinter Cell franchise have embraced 24-style action to go along with more traditional stealthy maneuvers, no other game in the series comes close to the purity of Chaos Theory's stealth playground.

Armed with a wide variety of gadgets and a trusty combat knife, you have everything you need to infiltrate a variety of multilayered environments undetected. You'll need them, too, because enemies react organically to your every move, spotting your handiwork well after you've moved on. To combat that, each level in Chaos Theory is filled with pipes to climb, hidden passageways, and multiple pathways to explore, providing you with a level of freedom few stealth games can match. And that's just the single-player - Chaos Theory also includes a brilliant competitive multiplayer mode (Spies vs. Mercs), as well as cooperative levels that require perfect synchronization.

Adding Deus Ex: Human Revolution to list of best stealth games can be a sticky issue, given that it forces players to go guns blazing into boss fights, even if they've otherwise been quieter than a church mouse augmented with hover technology. But while those forced battles are an unfortunate fact that can't be undone, Human Revolution's interpretation of stealth in every other instance is so strong that the good outweighs the bad.

While the game lets you customize the way you approach every challenge, protagonist Adam Jensen shows off the best of his abilities in stealth mode. Sneaking up behind guards and finishing them with a takedown puts his strength to better use than a gunfight, and can clear a room without a shot being fired. The cover system works well, letting you move seamlessly between hiding places. And where the brilliant Deus Ex inadvertently makes stealth easier with oblivious AI, Human Revolution has enemies that quickly spot you if you make mistakes. That means no dodging between cover while a guard is looking right at you, as it should be.

Sure, Dishonored does let you bust down the door of a mansion and use your powers to creatively murder every guard and unfortunate maidservant in sight... but there's something more elegant about sneaking through the one open window, snuffing out a single target, and sliding back out again without anyone realizing you were there.

Dishonored's stealth is also made more enticing by the fact that many of your dark abilities are meant to benefit a sneaky playthrough. We're talking a teleport ability that lets you juke between spots of cover, a power that disintegrates your victims, or x-ray vision that helps you map out guard locations while you're crouched on the roof. Get good enough and you can make it through the entire game without a soul outside your immediate circle - a badge of honor for any sleuth.

It wouldn't feel right to talk about stealth without mentioning at least one ninja. Mark of the Ninja is a 2D, side-scrolling stealth game, which puts you in the role of a master ninja (duh) defending his clan - which has had no contact with the modern world for centuries - from gun-toting invaders. Stealth is all you have to level the playing field but, thankfully, zipping between shadows is so fluid and sharp that it's a pleasure to take the job on.

Every ability in your low-tech arsenal is designed make sleuthing simpler, from darts that shatter lights to a panther-like crawl that helps you scramble up walls and squeeze through tight spaces. Each action flows naturally into the next, making every stage feels like a graceful, silent dance that you start at the beginning of the level. Far from fearing discovery, Mark of the Ninja makes you feel like a powerful stalker, a sense that few games <(a href="http://www.gamesradar.com/assassins-creed-chronicles-china-review/" target="blank">try as they might) have been able to replicate.

Amnesia: The Dark Descent is a great stealth game because it makes you terrified of being caught. You don't have so much as a sharp stick to your name when it punts you into the heart of a dark, creepy castle and tells you to watch your step. With no means of defense and little way to tell random ambiance from the approach of a horrible monster, you're left utterly helpless.

Terror is your motivator here, because you're facing something that can utterly destroy you, and you never know where it's going to come from. Being discovered is horrible, not just inconvenient, and the tentative stealth play that follows doesn't have to be forced. It just comes naturally, and never having to see the monster is all the reward you need.

The Thief series might not seem particularly remarkable these days. Its defining qualities are all pretty common for the genre - a first-person view, hiding in shadows to stay concealed, throwing objects to distract guards, and poking your head around a corner to see where your enemies are. None of that sounds remarkable until you find out that Thief is responsible for inventing those familiar mechanics, and that its best chapter, Thief 2: The Metal Age, still uses them better than most games that have come since.

Wide-open levels offer creative freedom, and the many different things you need to consider when developing a plan (how loud this particular patch of floor will be, or if you should club the guard in your path or try to sneak around) create a deep, complex stealth experience where few limits are imposed on how you play. It's by no means simple, but when you finally execute the perfect plan, you feel every bit the master thief the game claims you to be.

The hero of a stealth game tends to stay one step ahead of their pursuers because they’re predictable and rooted in patrols. That's what makes Alien Isolation so different and unsettling: the central enemy moves of its own free will, so you never know exactly where it’s going to appear.

In resetting your expectations for how a stealth game is meant to go, Alien Isolation forces you to relearn the basics. Moving slowly and quietly makes you better able to hide when there’s something horrible in the room with you. Even letting your guard down enough to walk into an empty hall can be deadly, because it invites doom from above. Hiding and crafting the tools you need to survive is fraught with anxiety, and being spotted by the immortal and hungry Xenomorph, after completing an intricate set of tasks, becomes painfully common. But there's no greater feeling than managing to make it to the next save point. Were you ever happier to see a pay phone in your life?

Snake Eater is the quintessential Metal Gear game, tip-toeing perfectly between stealth and storytelling. It's equal parts silly and melodramatic, diving deep into Cold War hysteria as viewed through Hideo Kojima’s lens of paranormal activity and self-aware video game-isms. But Snake Eater isn't just the ideal Metal Gear game; it's the best stealth game, period.

Snake Eater expands into unprecedented freedom, whether you want to Rambo your way through or make it to the end without killing a soul. Beating the game without leaving behind a body count is totally viable, thanks to your tranquilizer gun and a wide variety of camouflage patterns that help you inch past guards even in broad daylight. Snake Eater is also host to one of the greatest boss battles of all time: a multi-screen, hours-long battle of attrition against the world's greatest sniper. If you can wrap your head around the controls, you'll find that Snake Eater's construction still remains the pinnacle of the genre.