Patience is a virtue in the world of Deus Ex: Human Revolution.
On the surface you're getting a FPS/stealth hybrid with a sprinkling of RPG elements thrown in for good measure. Even though guns are prevalent, combat is not always the optimal choice. You wouldn't play Metal Gear Solid as a straight-up shooter even though it has guns; the same is true in this game as well.
The main mechanic present is choice: Do you risk getting into a firefight or do you try to find a way to sneak into that facility instead? Kill that guard or simply knock him unconscious? Are you sympathetic towards people when you talk to them or are you cold and distant?
During the game you will find special kits that allow you to upgrade your character. You can really customize him to suit your particular play style with all sorts of enhancements; from combat to stealth and everything in between.
I'm not even going to touch on the storyline with all its political intrigue, moral ambiguity and introspective questions you will ask yourself along the way. That's a whole editorial topic on its own. Needless to say, it gets quite involved as you discover more and more, but nothing that should go over your head.
I will warn gamers thinking this is a pure adrenaline rush type of game to pass this one by and don't waste your time. This is not a Call of Duty twitch-fest. This game rewards patient players and punishes impatient ones. In the same vein as Metal Gear Solid or Splinter Cell, it behooves the player to take their time and be aware of their surroundings at all times by tracking multiple guard patterns and avoiding security cameras and gun turrets; all of which will kill the impatient player very quickly.
Gamers looking for an intriguing plot and methodical gameplay will find plenty to love in Human Revolution.