I'd give The Simpsons Movie 7 or 8 out of 10. It was good, but the joke per minute ratio was pretty low compared to an episode of the TV show. It actually felt like the plot of a half-hour episode stretched over 1.5 hours. So the pacing was a little off. But when the jokes hit home, they were great. And it was entertaining overall.
I suspect they'll do better with the sequel, when there's less "Look! It's the Simpsons! On a movie screen! Look what we can do!" and more of the trademark humor that has sustained the show for a decade and a half.
Also, you will never in your life see more Korean names in a credit scroll outside Korea. Wow.