Superbad is a comedy focusing mainly on 2 friends and one day in their lives before they graduate high school in which their goal is to procure alcohol to impress their respective crushes. There's more to it, but that's the essential plot. But this isn't a plot driven type of movie.
First off I highly recommend you watch the trailer. If you've seen it and laughed then you should go see the movie. If you weren't crazy about the trailer then stay far, far away. Too often trailers have nothing to do with a movie or just show the funniest moments in an otherwise poor movie but in this instance its a good gauge to see if you enjoy the style of humor. I loved that its set in modern day but everything from the cinematography to the art direction was more late 70's-80's. Its odd but it works. The performances are incredible. You already know all these people and their comedic talents, especially Michael Cera from his "Arrested Development" days. Jonah Hill you may know from "Accepted", but if you don't, he's a great talent here. SNL's Bill Hader and Seth Rogen play 2 cops trying to recapture a little youth perfectly. Seth Rogan is also the co-author of the script and you can hear it in the dialogue. If you're easily offended by "bad language" you'll want to skip this one. In the beginning of the film I was reminded of "Clerks". The dialogue and the style are very similar but it turns into an all out classic teen R-rated comedy. There's a little "Dazed & Confused" style mixed in here. It wanders a little between characters and plots, and is really all about the jokes. This is a type of movie where there isn't really a scene you can point to and say "oh that part was great", its an overall work with every second packed with jokes and great dialogue. This is really a great comedy and if you can take it in as a whole you'll have a good time. I really enjoyed also that they took the theme of male friendship that is so prevalent in these movies one step further.
Overall I give it a 9/10. Its solid and funny and there's really no complaints I can make.