Your mileage may differ on this. As I type, the IMDB raters have this at an 8.1 rating, which is high. (It's #223 on IMDB's top 250 movies of all time, which is ludicrous.) I thought it was kind of smug and trite. But I stayed awake for the whole thing. So I'll bump it an extra half-star for me staying awake.
Set in the early 90's (according to IMDB), it centers on Charlie, who's entering his freshman year at Cruel Kids High School, somewhere near Pittsburgh. He has serious psychological problems, the underlying cause of which we know will only be revealed much later in the movie.
But showing Charlie as a rejected, possibly suicidal, loner for the entire movie would be boring. So after a few movie minutes, he gets accepted into the world of stepsiblings Patrick and Sam (Emma Watson!). They are sensitive seniors who drag Charlie around in their mad social whirl.
There are funny things. There are sad things. Good English teachers (Paul Rudd). Bad Shop teachers. Clueless parents (Dylan McDermott and Kate Walsh). Sympathetic siblings. Unrequited love. Girls infatuated with jerks. Easy availability of booze and drugs. And, of course, the big secret buried in Charlie's childhood.
Emma Watson is fine, though. Kept wanting her to say something like: "Y'know, this isn't at all like my previous school, Hogwarts. I was, like totally in love with this nice guy, Ron…" But no.