Yeah, during the tutorial you get a small taste of what is to come, but the tutorial in and of itself wraps up pretty quickly. In other words, no, it isn't nearly as long as the 7-8 hour "tutorial" from AC3.
As for the disc, if it's scratched or something - try using toothpaste. I once got a pre-used copy of Saints Row (I'm masochistic), that looked like it was drowned in Pepsi. Rubbed some reguar white toothpaste on it, wiped it clean and it played great... I mean... as good as Saints Row CAN play.