The 'present' part was the only thing that kept me playing Assassin's Creed, if it would only have been the Altair part, I wouldn't have finished the game because you just have to do the same over and over again. The game overall was a big disapointment, especially the ending.
To stay on topic: I don't like demo's, I look at previews and reviews to know wether a game is worth the money or not.