I've been a long-time Simpsons fan, but I agree that this movie was a poor effort on their part. I do indeed agree with most of the negative reviews, but most of the people who flame this movie aren't really that honest about it and don't give enough insight to really say what made this movie bad. So here we go, a much more honest review from a long-time Simpsons fan:
The storyline was really generic and like others say, it does seem like propaganda, but that's not why I didn't really like this movie all that much.
Animations were indeed spectacular, but I'll be lying if I said they weren't trying too hard to impress audience members, because let's not forget, a majority of today's typical viewers care more about animations than quality, which I find sad.
As for humor, this is the most important category, in my opinion. It was there, I did laugh a few times, but it was really lacking and I really felt it was trying too hard. Worst thing was that Homer was basically unlikable throughout the entire thing when he's usually a pretty lovable guy from time-to-time.
Overall, this movie was really average in my eyes. It had potential and just barely passed. If you're a Simpsons fanboy who thinks all Simpsons stuff HAS to be awesome and the best ever, you're fooling yourself, but who am I to say you can't enjoy it? If you do, go ahead. If you're a hater who never liked Simpsons in the first place, then just don't bother commenting on, let alone watching, this movie in the first place.
That is all.