as a long time simpsons fan, who wanted it to be great, i thought it was absolutely terrible, i laughed about 3 times and possess at least 50 better 20 minute episodes...it just seemed to be lacking in laughs - and worse still completely the opposite of what made the simpsons so great in the first place. My housemate said "its only a cartoon" and that to me is the biggest problem, because, the simpsons was'nt "only a cartoon" and thats what made it great.
To me its problems were -
1. An absolutely ridiculous plot, where the hell did they think of that - there is stupid (clown college etc) and there is outright stupidity (the residents of springfield get put in a massive snowglobe and decide to hang the simpson family, the epiphany, on the run, the massive TV screen, the bomb)
2. Despite the fact that every single member of springfield was in it, how did they manage to actually get so few people in it? other than Moe, barely anyone got any screentime with most characters not even saying a word. I was actually left thinking harry shearer hadnt been involved, because other than mr burns, very few of his characters appeared.
3. Dr Nick's Death
He wasnt in the film, other than to die - fair enough killing off maud and bleeding gums murphy, but doctor nick is a consistently funny character, it just seems they put it in to shake things up.
4. Homer is just starting to border on retarded now, he has nothing in common with the homer of the first ten series, he is just an absolute idiot who gets more selfish and idiotic by the minute, not at all the family man he was
5. how many more times is bart going to think flanders christian lifestyle is better than his relationship with homer? they have used this so many times now.
6.Arnie shouldnt have been president, Mcbain should have been, especially when the point of mcbain is to be exactly like arnie. seems that was a missed trick to me......
7. The stupidity of the plot again.......home riding upside down round a massive dome and then riding down on waves of glass, the boob indian women, the epiphany with him melting, the unnecsecary violence (rock and the hard place etc, lisa punching bart), colin - what was the point in him, yet another person/stereotype for lisa to fall in love with, Bart's penis (why, why, why?), The complete destruction of springfield
8. The animation - admittely it was beautifully done, and did look amazing BUT its not the simpsons, i got the feeling that if the film had been animated like the TV show, then there would of been a lot of overlong shots. I actually think they used the animation to fill in the gaps in a lot of places
It just seemed completely detached from reality, and the thing that made simpsons so great was the fact it was a cartoon, but with a lot aspects of reality, but the film just seemed to contain nearly every single feature that has made the cartoon so bad for the past 6 years.
sorry about the long post but its just the most disapointing film i think ive ever seen, when it should of been one of the greatest, if this is the way the simpsons is going i genuinely hope they knock it on the head, and in the meantime i will have to wait for futurama (which can get away with being stupid)
i think the only joke i remember is "look, stop this, we cant keep pulling up at every sop, did-and and wun wey sign we drive up to" - that seemed like a typical simpsons joke. Made me laugh anyway

that and the crashed ambulance on the top of springfield gorge, which i thought was a nice touch
edit: just read empire's review, and word for word it is absolutely spot on - they never needed to make a film