I've never been a "hardcore" Simpsons fan, always just catching episodes here and there for the past however many years it's been on. Even watching the show in this fashion I've noticed the decline of the show. For me though that's been going on for awhile, in the earlier episodes they focused mainly on Homer, then they sort of switched to Bart, then they came back and did a lot more of both of them together. I liked the focus being mainly on Homer, which is why I loved the movie so much, in my mind that's what makes it a return to the original.
I thought the movie was hilarious, there were so many great one liners, the plot was strong, there was plenty of emotion, self-discovery, and a great resolution, what more do you want from a movie? Well everyone is entitled to their opinion, and mine is that this movie is awesome.