I'm currently playing part two and haven't run into any problems with the original game or the second one. Second game is the beginning of the UPLAY stuff, doesn't seem too intrusive though. Games have native 360 controller support too if you own one.
I just finished AC1 yesterday and started up AC2. AC2 runs far worse than the first one, pretty disappointing. When I say far worse mind you, it's no longer 60fps 95% of the time. In the first town I've been as low as the mid 30's. Now anything above 30 seems like it would be fine, but it's very jarring fluctuating between 30 and 60 a lot, makes it feel worse than if it was at 30 all the time.
Changing the graphics options has zero impact for me on the framerate too, which is really odd.
AMD Quad 3.0
8gig memory
460 gtx oc
win 7
I hope brotherhood/revelations runs better than this.