Second of all, I think AC2's ending has to go down in history, alongside the Star Destroyer bit in Force Unleashed, as one of those gameplay moments that sounds absolutely spectacular written down but is actively horrible in execution.
I actually kind of enjoyed the game itself up until I realized it wasn't ever going to get any harder or more varied (which, luckily for me, didn't actually hit home until just before the ending). It's better than the first, as little as that is saying -- the new structure helps things along, but more than that the fact that every single assassination mission is different from every single other assassination mission. To some degree.
The game is still nowhere as good as it could and probably should be, though. I really liked climbing towers to find viewpoints until I realized many of the towers were exactly the same. I really liked the fact that I had new ways to deal with guards and the crowd, until I realized almost all the groups you can hire are identical to one another (no difference between a whore or a thief luring a guy away). I liked the new items Ezio could wield, until I realized that the combat is so easy that you never feel even remotely obligated to use any of them other than the wrist-shanks.
I still maintain that AC's combat should be really, really hard in order to encourage stealth and running and chases and all the items you've got -- like how MGS3 on normal mode is kind of boring, but on extreme it's a goddamn revelation.