Counting myself as one of the many people who has seen every conceivable Simpsons episodes countless times, I went into this film with some trepidation. After all, even the most generous fan would consider the last...ooh...5 to 10 years worth of episodes just 'not up to snuff'. There have been moments, but nothing next to the random anarchy of seasons 3 through 6. So with that frame of mind, I was pleasantly surprised.
The Simpsons Movie offers one of those bittersweet things for fans. If you are a fan of the show, you've put up with worse, and this is certainly better than the last few seasons. While it may not be as fresh as it was 20 years ago, it is still bloody funny. Many critics have said this "doesn't take enough risks", but I disagree: a Simpsons film after 20 years on the air could have risked alienated jaded fans even more, but instead it has restored the faith of many. If I wasn't outright laughing, I had a smile on my face throughout most of it.
Long story short, if this wasn't a Simpsons film, it would be hailed as one of the better comedies of the last few years. As a Simpsons film, it still deserves that mantle as it does what the show has forgotten about in recent years: for every bit of dumb comedy, you need to remember that the heart of the show is the family. In many ways, this has helped expand it into audiences who wouldn't normally appreciate the show.
If you've listened to the commentaries on the DVDs for the show, which are even funnier than the episodes sometimes, but the writers can sometimes come off as aloof and dare I say, arrogant. They view "fan" criticism with contempt, and often take it personally. They spend some time explaining jokes they think the audience didn't "get" and defend the declining quality of the show by saying every generation has its own few seasons to enjoy, and those that enjoyed the earlier years will look back on seasons 7-18 fondly one day (perhaps around the season 25 to 29 mark???

) However, that defensive attitude seems to be absent in this film, as it is all about pleasing the fans with in-references and layer upon layer of gags.
It isn't perfect, but it's better than 99% of the other films I've seen lately.