Indeed, it seems like they had the most larger then life story you can ever make, how to contiinue with something relevant or comparable after that? Anything else pales to it (and thats why the shows creator left, nothing he wants to do). But yeah I immadiately thought Chuck is God too, but I doubt it, dont think they would show us God, but how he vanished was real odd, indeed hints to that possibility for sure.
How did Sam survive? Odd cliffhanger. And yeah I dont expect next season to be good either, but if anything I expect one storyline, a bit of a reversal, when Sam gets back, because he has to, he will be the one going back to "hunting" and such, while Dean will want to have a normal family life and such, Sam prolly trying to convince him otherwise, like Dean did in first seasons to him.