Assassin's Creed II is a completely different story entirely. I still found myself losing out on sleep, food and most human contact for hours on end, but unlike my missions throughout the Crusades, I relished every moment of my adventure through Renaissance Italy. AC2 is a polished game in every aspect and a great example of the iterative process. Nearly everything wrong with the original has been reworked or replaced with something more functional.
At E3 2009, Ubisoft made a big deal about its foray into the visual effects field, and AC2 is a good proof of concept they're heading in a logical direction. The environments are varied and look great, particularly when surveyed while perched atop a cathedral. However, it was the little details that really made me take notice. AC2 features some of the best facial animation this side of Uncharted, probably better. Coupled with the excellent voice work, it helps give characters more personality. Compared to Altair, Ezio (AC2's protagonist) has a personality, marking one of AC2's bigger improvements. It's great to actually have a character that isn't just a generic brooding mess, but someone with some sort of depth. Granted, Ezio isn't exactly likeable, but that's part of the game's magic. You grow to like the guy over time and even sort of sympathize with his journey.