The more I've sat on it, the more I think the ending was a lazy cheat.
If the showrunners wanted to kill Dean, or Sam, or both, they should have had the balls to do it without a sure-fire promise of New and Improved Heaven. If they wanted to go for bitter-sweet rather than sad, they could have given a glimpse of heaven, or maybe just the promise that Dean was in heaven (as they did in establishing Cas had gotten out of the Empty). But it shouldn't have been more than that. For all its detours into other realms, this was ultimately a show set in and concerned with the problems of this world,