Just finished playing through ACII tonight. It was really fun at first, but towards the very end it started to get a bit annoying and repetitive. That being said, I'm going to start playing through Brotherhood tomorrow, because the story is pretty freaking epic. Overall, it took me over a week to play through it all, and I hardly got bored, which is a very good thing coming from me. I haven't really enjoyed gaming as much lately, especially single player, but this was easily an exception.
I bought all the games except the first on Steam for super cheap a few days ago while they were on sale. While I'm sure the PC versions are far better, I have to admit that the controls definitely feel like it's a port from a console game. The whole targeting system, and especially menu navigation, feel totally out of place with a mouse and keyboard... but I like my 1080p with 2xAA at 60fps.

The trouble will be waiting for the late November PC release of ACIII, but I still have Brotherhood and Revelations to play through first so I think I can manage.