Ending is great, it could be spoiler of some sort, so I'll write it in white ;p. Don't read it if you didn't finish AC:
The ending proved what does it mean "nothing is real, everything is permitted", gave an impression that not only the virtual wold in animus is not real, but also the thing we consider "reality" isn't. Sorta Matrix-like philosophy, which I love, cause if you believe in it - it makes you worry less, and fear less about some actions that you do r-l. Not that I am sure world is an illusion of some sort. ;] Maybe it is, maybe it ain't. But it makes me wonder, and such mental "stimulator" is pretty fun, and maybe challenging in some ways.
Re-fighting every boss at once was good idea too,
and that "eagle-sight" that main character gets r-l in the end makes it possible to expect that such fights and all the Assassin's creed-like action game to be set in the times that they consider "present", world they consider "real".
Game is epic win. ;]
Multiplayer would be sweet, templars vs assassins, gta4-like.