I bought Deus Ex Human Revolution on christmas (~ 6 months ago). I didn't really get a chance to play it due to school and what not. Now that it's spring/summer I've played it for a substantial amount of time and I have to say, it's incredible. The sheer depth of the game is amazing. It's completely non-linear. You could cause a riot by shooting everything in site, or you could sneak around like solid snake, totally your call. Also, this is the first game I've played where it felt more satisfying / fulfilling not being a maniac. I'm about 60% through the campaign and as far as I can tell, I haven't killed a single person.
As far as complaints are concerned, I only have two: (a) This game is too easy. (b) Retarded AI (kinda tied to a, but there you go). Part of the allure of stealth games, is that they inevitably devolve to a battle of wits (you against the computer). When there's no challenge there really isn't any fun. I am playing this game on the hardest setting and I am yet to hit a roadblock. It's too easy. The computer controlled AIs do not act like you'd expect a reasonably intelligent human being to act, so in a way I feel like I am cheating. The only stealth game I ever played where I felt the challenge was just right was Metal Gear Solid Peace Walkers (that's the only Metal Gear Solid I've ever played). I remember trying to play the first Splinter Cell (stealth action redefined) and I failed to complete it because I found the difficulty took away from the fun (on the upside, the AI was more realistic as you couldn't really knock somebody out and leave them there because somebody would always find them (as should happen).
9/10. 10/10 if the difficulty had been tweaked.