I recently finished reading The Perks of Being A Wallflower. That meant I could finally watch the movie. I was really excited about the movie because I love Logan Lerman and Emma Watson. I was also really interested in Emma Watson's American accent (she did pretty well I thought).
But for me, my favorite part of the movie turned out to be Ezra Miller who played Patrick. He was seriously perfect! But I'll get back to that.
I had never read Perks before, and as a seriously shy introvert in middle school, wish that I had read it then. I thought the voice was a little young for high school, but I got used to it as the story progressed. In the book, I really got the sense of Charlie's, for lack of a better term, simple-minded nature. Everything was black or white to him. He didn't really understand the concept of lying, even for a good cause. He liked following the rules because it meant he had a handbook for the situation. He was pretty socially awkward. But he noticed everything and understood what people liked. He was a great listener.
And those things that I liked in the book, didn't really show up well in the movie. I thought Logan Lerman did a good job as Charlie, especially in the end scenes, but it's just really hard to see someone noticing other people in movies. It didn't translate as well to film. At one point Patrick states outright that Charlie notices things and that he's a wallflower. It wasn't subtle, but it got the point across for those who didn't read the book and knew the nuances of Charlie.
Patrick is the largest character in the movie and I thought Ezra Miller played him perfectly. He was funny and not too over-the-top, but endearing and genuine. Plus seeing "Bland" as Mary Elizabeth was cool. I thought she did a really good job in that part, even though that's not at all how I pictured her. One of those times where film did it better than my mind.
So I would say, def read the book first, then see the movie. Both are good, but you'll get a lot more out of it if you read the book first.