these games all seem to have so much playability too. they are always the last games on my shelf that i think to myself "i havent beat those yet". halo, cod, etc... all beaten in a week or less. ac 1 took me around a month, and ac2 is taking me a bit more than that, because there is just more to explore, more ways to kill people, and more side missions.
edit: i will say though, i very much hate the last boss in ac1. they made it difficult in an annoying way...