Just finished DE:HR last night, impressions(spoilers):
1) Really disliked the XP bonuses for stealth, felt like the game was punishing me for playing it any other way than how the designers intended. If I want to play a bloody murderer I shouldn't be penalized for it. (and no, the 'headshot' bonus is still less than the 'moral' choice). Min/Maxers hate this kind of thing. This is Deus Ex, not Thief 4 (I like thief, but if I want to play thief I'll play goddamn thief)
2) horrible...horrible ending, boring luddite vs. 'the man' decision...DE1 tackled more interesting themes better.
3) cheesy use of name dropping 'the illuminati', 'triads' etc., DE1 did a vastly better job introducing these.
4) hated getting winded while sprinting
5) hacking was lame
6) too few weapon mods and you get them too late in the game
7) found the plasma rifle way too late, got to use it...once at the end
8) Inventory was a pain in the ass...
9) had to eat candy bars to regen energy, instead of the regen mod going past 1 cell
10) I must have used quickload about 400 times because there's no way to accurately anticipate what the game actors will do. I wouldn't have cared if I didn't lose 30 xp each time!
The best fun I had was when I just said 'fuck it' and slaughtered the entire police force during the riot and sold their weapons to the black market guy. Actually...that was the only fun I had playing this game.
I'm glad they made the game, and I'm glad it was commercially successful so the genre gets more funding, but bleh.
