I've so far had very few issues with the game.
I did manage to assassinate a character I wasn't supposed to - there is a mission where you chase someone after talking to him. You catch him and he apologises, he has your father's axe.
As I was chasing him the assassinate option came up, which I accidentally clicked and the whole game just hung on a black screen. Reload last save fixed that.
I've managed to fall through a piece of scenery - my character just bouncing up & down with no way to escape.
Finally, the anomalies - found my first one, went to try and do it and the light beam generators were in such a position it was impossible to get past the second block. This was an acknowledge bug in the Ubisoft forums, so I'm hoping that one is fixed.
Really pleased I picked it as one of my launch titles.