Game is awesome.
I wasn't expecting much and i hadn't really followed its development cycle; i knew i would buy it anyway since it takes place in more or less my home town, for a significant part, but wasn't too thrilled.
I didn't think AC1 was utter crap (it wasn't) but i couldn't put more than 4 or 5 hours in it, and lost interest as soon as i unlocked all towns. I realized its potential, but it was plagued by extremely repetitive missions' and the same problem which affected most Ubisoft sandbox games; they put you in a huge open world filled with absolutely nothing to do, or nothing worth doing at least.
There was no reward to exploring towns and doing side quests.
During my first 8 hours with the game AC2 kept throwing new stuff at me; sub quests, side quests, different mechanics and decent rewards, new items and abilities for Ezio. It almost became overwhelming at some point. My only complaint would be most (all ?) abilities you learn are linked to your progress in the main quest; i would have liked some advanced techniques to be optional and acquireable (?) through sub/side quests, which would have further encouraged going for a 100% completion.
Also liking the story so far. I believe most players are not familiar with historical events depicted in the game, but they're surprisingly faithfully recreated.
What the developers did was creating links between unrelated events in italian history and make them appear like the 'visible' part of the same, larger, invisible (and fictional) conflict between assassins and templars. Very Dan Brown-ish, but also very clever.