UE3 does a fine job with the game, runs like a dream and load times are so quick. Why would anybody want them to use Idtech 5? That engine is terrible.
Game is ok but I find the stealth aspect extremely basic and limited, The AI is decent but lots of room for improvement. Played it twice, once mostly stealth non lethal for low chaos and them second time kill everybody on very hard. Interestingly enough the very hard kill everybody playthrough was easier and shorter. Teleporting assassins and tall boys were the only real challenge and there are hardly any of them.
I really thought more things would change in the world playing high chaos and doing things differently. I liked how the last level changes atmosphere and resolution but there aren't many other changes, certainly very few big changes. Compared to Deus Ex HR the options are minuscule. Compared to Bioshock, the powers and narrative is mediocre. Compared to Thief: DS the stealth is poor. I guess what I'm saying is that it's really nothing amazing although I like the clean and distinctive world they created. Voice cast has some big names but underutilized.
I wasn't really following this game much before release, Blink is a cool feature but I can't see how this is 91 on metacritic.