Just finished it. It lasted 13-14 hours, didn't do everything though (didn't collect all the runes).
I liked the game, the setting was very nice. The gameplay was great, very open-ended, a ton of things to do and every mission was able to be done in a few different ways. I went for low chaos (bar the first mission when I killed a lot and got high chaos) so in the end I got the good ending.
Generally in the first few levels I explited roofs, while later I did that but also posession was great when I was in delicate situations.
I didn't like AI, in fact I thought that it was poor. Even ancient games like Deus Ex or System Shock 2 have better AI, IMO. I thought that the story was very mediocre. THe 'twist' was predictable.
I'll put the game at around same level as Human Revolution but quite below BioShock/System Shock 2, and way below Deus Ex. Still a great game, and I am happy that I played it. 8/10