I have just finished watching all 18 of the series episodes of The Inbetweeners. I will probably watch the movie at some point; and why not? This was a brilliant show, and as a latecomer, I feel blessed because I did not have to wait for new shows. That must have been agony.
First of all, the cast is perfect. Their chemistry is without peer; the next best thing that I can think of would be The Kids in the Hall.
Second, the stories are a run through every non-cliche you can think of. There are more ideas in this show than you would get from any American sitcom.
Third, there is no way to translate this to an American audience. The show is too real. Americans simply could not handle any of the graphic sex, the drugs, or the lawlessness. Even in the post-Borat world, there's no chance an American audience would be exposed to anything remotely like the British series.
Good luck with that.