Perks of Being a Wallflower is one of those culturally important books. I mean, sure, it's pretty much just a modernized Catcher in the Rye, but it's still a moving and powerful tale of a truly messed up kid just trying to be normal.
It's not a perfect book, but it's a quick read with an intriguingly flawed main character. And the film adaptation is actually written and directed by the writer of the book, so it fares much better than most adaptations.
Despite the same writer, there are quite a few subtle differences between the film and the book. The movie is much less depressing; it takes the incredibly messed up Charlie and turns him into just a kid with problems, when the book is so much more complicated than that. This isn't necessarily a bad thing, though, as Logan Lerman pulls off a great performance despite the slightly neutered role. The other leads, Emma Watson and Ezra Miller do a fine job, but they aren't given as much to work with, and sadly Paul Rudd as the teacher who takes a liking to Charlie is pretty much nonexistent.
Given the tone of the film, it's easy to see why they went for a comparatively more light-hearted affair than the book. This is one of those movies that gives you that feel-good buzz when it's over, and life-affirming movies like this are what make film such a powerful and enchanting medium.