Assassins Creed

I don't want any spoilers (though I'll probably get some on here) but does AC really end when your done with the chain of memories or do you start playing as Desmond or something?

I read a review that said you could plow through it in 20 hours. Well I had about 7 or 8 hours in and i was on the second to last memory when I went on vacation.

Thanks

The final memory is the end of the game.  You get to wander around afterwards and use the animus for replay.  Hack some computers as well, but that's it.  It's a big letdown actually.