It's hard for me to be objective about this movie because reviews and clips have spoiled a lot of the jokes and plots points already. Perhaps I should've known better. Then again, I didn't have a lot of faith in the movie, so maybe that's why I wasn't more careful.
But I am fairly confident that this is a good movie.
Is it as good as a classic-era episode of the show? No, because it's a movie. The Simpsons in its purest form will always be those half-hour pieces of comedy gold from 1990-1997.
Is it better than the new episodes of the show? HECK YES, and that's because the writers and voice actors stayed true to the characters. I can think of possible ways the plot could've been better, maybe focused on Springfield a bit more, maybe not gone to Alaska, maybe given more time to great characters like Mr. Burns and Principal Skinner, but in the end what makes this movie worth seeing is that the characters are handled well. Their dialogue feels a lot more real than it has in years.
And it sounds real, too; I concur with the people who praised Julie Kavner's performance in Marge's farewell tape. It was, honestly, a surprisingly good performance. (It would have been more surprising if I hadn't read about it in a review earlier, and no one's sure where she got the video camera from, but -- whatever.)
And that brings us to the topic of Ned Flanders. He is BACK! Finally the writers have remembered that Flanders is supposed to be an enviably perfect neighbor who loves his fellow man to a sometimes annoying extent, NOT a fundamentalist bigot. I also liked his introduction into the story: you would expect him (especially after these recent seasons) to be angry or at least somewhat disgusted at Bart after the stunt he pulled, but instead he's the only person in town who shows him some compassion.
Some other good plot bits were the callbacks to the sinkhole and the motorcycle, which is the kind of clever writing you usually only see on American Dad these days.
Most of the gags were very good, although there was nothing truly classic that made me laugh hysterically, unless I was just spoiled by seeing and hearing about a lot of them. And the more newish awkward, confusing, unfunny stuff was mostly absent, rearing its head only in a few of the Alaska scenes (Boob Lady, for example).
So in conclusion: thumbs up.
You can say G--damn in a PG movie. The (un-detailed, cartoon, nonsexual, child's) penis and the middle fingers do help push it up to a PG-13, though, although they're not exactly deal-breakers.