Its a common conception among many PC gamers and developers alike that stealth games are one of the hardest genres to pull off properly. The "bad stealth level" is a despised gaming cliché because most developers that try to implement it properly just end up failing miserably. It’s much easier to create a conventional action game where you shoot everything in front of you rather than to try to make it fun and challenging to evade enemies rather than blast them into little meaty chunks.
Even the best game designers tend to fail at making it easier to sneak around enemies than it is to get rid of them. In order to create a complete stealth experience, the developer has to make the enemies respond realistically to sound, sight and other stimuli without making it absolutely impossible for the player to accomplish their goals. It has to be challenging enough to create tension, but not so much that the player either gives up entirely on the game or just decides to take the Doom approach with things.
The artificial intelligence needs to be believable, but not realistic. In reality, few could manage to recreate the sneaking feats of video game stealth heroes without some truly fantastic luck. The enemies need to give some kind of feedback to the player when they’re about to spot them, but not so much that it makes it trivial to remain entirely hidden from them. Artificial intelligence has historically been one of the most substantial development challenges. We’ve seen continued advancement in graphical technology almost every year, but artificial intelligence remains mired by the same challenges – particularly as developers need to continually re-develop new engines, generally with an eye on keeping the graphics close to the cutting edge.
When properly executed, a good stealth game rewards the player for making their way through the environment without disturbing the various mobile enemies. An atmosphere or rising and falling tension is created. The player is encouraged to be patient, waiting for the perfect time to evade a patrol, dodging between shadows, obstructions and through foliage. Many stealth games also emphasize non-lethal gameplay, letting the player dispose of enemies by knocking them unconscious or distracting them rather then simply sending them to a bloody end. Although in gameplay terms it makes little difference whether the inert enemy is "dead" or "unconscious," it helps to implant the idea in the player’s mind that using less violence to accomplish their goals is considered an additional and praiseworthy challenge.