It's not brilliant but it's big.

...
The Simpsons Movie suffers from the weight of its own legacy, an unwieldy plot, and a killer sight gag that was too big too soon.

A few minutes into the movie, you realize that for this thing to work it's got to be better than or at least in some way different from a TV episode. But after 400 installments of some of the best comedy TV has ever seen, it's instantly clear that the bar has been set too high. There's also the problem of the unfolding plot. It's about the environment? Really? Good luck going to town with that one. Then the much much-buzzed Bart full frontal turns up in the first fifteen minutes. I must admit I've never laughed in a moviehouse harder this year. It's truly one for the ages. But it dooms the next 75 minutes of the film -- the momentum isn't sustained (see plot, above), none of the next gags comes close and it ends up as the film's defining moment.

So, besides a big, fat, juicy "D'oh!", what else is there to say of a film whose saving grace is a wiener shot? That even if you turned your expectations down a few notches, you'd still be disappointed ("I hope there's cameos!"). That it's a movie that didn't have to be made and that movies of TV shows rarely turn out great anyway. That maybe the filmmakers knew all this going in so they didn't strain themselves. That since Homer (speaking to the audience) laid it all down nicely for everyone at the opening scene, no one has the right to bitch about anything.