I really enjoyed the movie, and I was laughing through most of it, and I even applauded a number of times when they had a particularly good gag. They didn't take it too seriously or try to do something different because it was on the big screen and actually get self-referential at times. There are a lot of individual bits/gags, and there's of course a story that tries to tie everything together, but the story itself isn't really what the movie is about. There are a couple of side stories that were really sweet.
The relationship that develops between Bart and Ned Flanders makes sense, and it was cute to see a different side of Bart. The hot cocoa scene was awesome. And the whole storyline with Lisa and her new Irish boyfriend was cute too.
There's one particular scene that will probably be the most talked about, which is why I find it even more annoying that two reviews I've read mention the bit in their review - BOO to them for giving away a major spoiler.
When Bart is skateboarding naked through town, they throw every manner of obstacle to block his private parts, even things that make almost no sense, but it's hysterical along the way - which is what makes the payoff when they actually show *everything* even funnier. It's not a plot point or anything, but it's a great bit.
There are bits that go a bit slowly, but they don't last too long, and the rest of the movie definitely makes up for it. The movie reminded me of "Airplane" in the sense that I missed lines here and there because we were still laughing from the previous line, so I guess that's the reason to see it more than once. And there are a lot of background things to look at that are funny too. There is also one point that will be very satisfying for long-time fans.
This is really more of a technical point, but I'll put it in spoiler tags anyway.
Even though there's a regular cast crawl later in the credits, I love that the beginning of the credits show the actor's name and then a picture of each character that the actor voices. Showing it visually that way gives you much more of an appreciation for how much some of them do for the film.
And for those who leave as soon as the credits start - don't.
There are two Disney connections.
They unsurprisingly skewered Disney in one scene where Bart has a black bra on his head and says, "Look, I'm the mascot of an evil empire." And then, one of the voices in the film is that of Russi Taylor, better known as the voice of Minnie Mouse!