I thought the movie was really good but i can see where some people might not like or not get the humour. Only recently turning 21 and still having alot of the same friends from high school (some of which i've known since 1st grade) it was easy to relate to the type of angst the two main characters dealt with and the how it felt having your best friend go to a different school, as well as the type of humour that went with it.
The way they portrayed high school seniors came off as very real to me, the situations, the dialogue, everything. When compared to the almost realistic group of horny guys from a movie like American Pie, or to the never realistic portrayals of teens in movies like She's All That, Superbad is one of the realist movies i've ever seen. The humour comes with being able to relate, so if you think you're to old to sit around with your best friend and just curse for the hell of it and yell at each other for no reason then no, this movie isn't going to be funny to you. Yes it is sophomoric but its not like its nothing but fart jokes, it's just angry/bored teens saying and doing really dumb and messed up things. I think anyone that had a normal childhood can relate. Of course if you were a bit of an outcast you'll relate with the characters a little better but you don't have to be cuz even the popular kids had that one guy in the group that would mention how a girl looked in a really funny way (in most of the adds one of the characters brags about how he saw some girls g-string thru her pants, who hasn't had a friend like that?)
as for the ending... I'll be honest, at first i didn't like it but the more i thought about it the more it grew on me. Normally i watch this type movie and like to have everything wrapped up at the end but with this one they didn't do that. I won't give it away here, not that it matters its not like i'll be spoiling plot twist, i'd just rather anyone who might see it themselves experience it and make their own conclusions.