The look didn't seem much different to me, a few tweaks here and there but essentially it looks very similar. It does have less screen tear, though, better fps and I'd say there seems to be more people/detail on-screen that in AC1.
It's not a big leap visually, really. Seems like all the effort went into content, missions, etc. - which is no bad thing as I thought AC1 was average at best due to gameplay weakness, which thankfully AC2 doesn't have.
Try to be reasonable... its easier than you think...







