Or about as buggy as Lair, anyway. In 10 or so hours of playtime, the game has frozen mid-game once (literally frozen--Altair was floating mid-air and the peasants were as well, while I could still pan the camera around but not open up any menus). It has also been unable to load (taken over 5 minutes before I quit letting it try) three times. It's also taken over a minute to actually load at times. This is what I consider to make the game very annoying to play. Additional problems that don't preclude playability: Very frequent glitching with lighting (particularly trees and other complex stuff), SEVERELY bad antialiasing at times ("pixels" four or nine pixels large), FPS lag in intense areas (which is most places).
As highly anticipated as AC was, and the lack of such comments in reviews I've read, I'd expected the game to be more polished.