The Inbetweeners is the bastard child of your typical Channel 4 "with it" mentality and the movie "Superbad". It borrows from the latter a bunch of central characters, all boys, who are desperate to party, get drunk and get laid. It borrows from the former a desire to be cutting edge, quirky and hip to the kids...in short, comedy guided by middle aged channel execs.
It can be genuinely funny, particularly in the first episode where the boys try to exploit some obscure licensing laws in order to buy drinks in a pub and the aftermath where the nerd character outs all the school kids who are underage drinking. It can also be muddled and packed full of repellent characters who are more annoying than funny. What could be a well developed growing friendship between the two main characters, a nerd who's family have fallen on hard times and has moved from a private school to a state one and the boy assigned to be his "mentor" against his will, is never fully realised as the show is too keen on showing all the kids partying and generally behaving in gross ways. It's like Channel 4 have seen Superbad and missed the point of the friendship that underpins the movie.
Also the parent characters are very poorly developed, as you might expect in a movie like this. Again, they've taken from Superbad the idea that one of the characters has a hot mum all the other boys want to screw. Not only that, the actors playing the parents all seem to be in their early 30s and too young to have 16 year old children.
But like I said, it can be very funny when it doesn't try too hard to ingratiate itself with its target audience. Oh, and it's way more watchable than "Skins".