I just finished the game. Aesthetically, it's fantastic. The expansive landscapes and attention to detail is simply breathtaking at times. Controls for the most part were fluid and intuitive, making for an excellent parkour simulator when combined with the massive cities. For that alone, I'd recommend this game. Just trying to reach as high as you can go or getting from place A to B without stepping on the ground is so much fun.
Combat wasn't bad, but it wasn't anything special. The high-profile assassinations (where you lunge, tackle, stab) never gets old though

. The missions are pretty repetitive, but oddly I was compelled to save all of the citizens and do all of the investigations (even though you only needed a few to move to the assassination). The ending was a bit of a cliffhanger, one which you understand more if you were persistent and investigative throughout the game, which decent bit of a twist. I can't wait until the sequels (I read it was to be a trilogy).
The two things that bothered me:
Beggars. I hate them with a burning passion. You'll be sneaking around and suddenly some stupid wench is all up in your face, hindering your path, "Please sir, spare some coin". No, F-you, I've got a job to do. Then there's the super-poor that push you when you walk by and continue to push you when you get up, usually blowing your cover. I throw those suckers into walls.
Water: A world-class assassin, fighter, and gymnast can't tread water. There's a part in the game near water and those freaking pushy beggars are around. I died and had to restart that mission at least a dozen times. ARG