Meh, I killed just about everyone, but got everywhere stealthily, I snuck around, saw what everything was, found almost everything, killed almost everyone. It becomes FAR too easy, randomly stand on pipe, blink behind someone, kill, even if 10 guys rush at you, blink out the way, and then kill them anyway with whatever the hell you want. At first I tried to kill stealthily all the time because of health, weapons, powers, etc. Later on I just couldn't be arsed, I still went "stealthy" but wasn't bothered about waiting ages or being careful, if I get seen, everyone dies quickly with a nade or gun, if I don't, blink to the next guy, rinse repeat. Way too easy.
Ending was anticlimatic and overall.... I dunno. It was fun for a while, the mechanics of moving around were good. Stealth is fine, I'm not a massive fan of stealth games, 99% of stealth games are just waiting a long time for the right moment to move.... waiting isn't fun, simple as that. Powers that make stealth fun is a great idea and this game got that spot on. However they also made it too easy, as with basically every RPG I think I've played in the past 5 years, you start off strong, and become "uber" far too quickly while the enemies don't scale.
FO3 wasn't too bad, while you could go anywhere anytime and find things impossible to kill and scaling wasn't great, there were still difficult guys to kill at the end and really all the way through.
Bioshock, Skyrim, this, etc, etc, yes its hard to explain why you'd be fighting uber soldiers further into the game but that is where the hard part of writing/designing a game is, soo lacking lately in games.
I think I spent the final 1/3rd of the game playing to finish rather than playing for fun. Blink, stab, puff of smoke, blink, stab, puff of smoke.
I think one of the main things it lacked was some kind of boss style baddies, there was really only one in the entire game that I can remember, and tallboys which are just far too much bother to kill so never even bothered. 4 types of enemy really, of which 3 were very rare and one was so easy to avoid it was silly.... that just doesn't cut it.
It's MUCH better than loads of other games in the past few years, but still has massive flaws. Story was decent, though frequently very very obvious what was coming, powers were good in theory, though much like Bioshock I barely used time/rats(at all)/wind, dark vision/blink are all you need and give you unlimited power usage basically.