Okay, I made it through a little more than half the book, then skimmed the rest. I went from curious to amused to outright offended.
The bold stuff is mine.

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I am writing to you because she said you listen and understand and didn't try to sleep with that person at that party even though you could have. Please don't try to figure out who she is because then you might figure out who I am, and I really don't want you to do that. I will call people by different names or, generic names because I don't want you to find me. I mean nothing bad by this. Honestly.
...
I have finished To Kill a Mockingbird. It is now my favorite book of all time, but then again, I always think that until I read another book. My advanced English teacher asked me to call him "Bill" when we're not in class And at this point, it becomes "really" obvious that Charlie is a self-insert character with a teen TV-movie cool English teacher. and he gave me another book to read. He says that I have a great skill at reading and understanding language contrary to the fact that I'm evidently at a 3rd grade writing level, and he wanted wants me to write an essay about To Kill a Mockingbird.
...
This boy who likes my sister is always respectful to my parents. My mom likes him very much because of this. My dad thinks he's soft. I think that's why my sister does what she does to him.
NO.
It's page 11 and I'm already annoyed. I don't care that these are supposedly impromptu letters to an anonymous therapeutic friend, this style is clumsily executed and I shouldn't have to read these four sentences four times in a row to understand what the hell he's talking about.
...
Now, as a rule, high schoolers in novels never act like any of the kids you knew in high school. Stephen Chbosky must have been homeschooled, or a complete, hypersensitive, weirdly omniscient freak like Charlie (sorry) when he was a teenager. Example.
...
I feel very ashamed. I went to the high school football game the other day, and I don't know exactly why. In middle school, Michael and I would go to the games sometimes even though neither of us were popular enough to go. Awww, I feel soooooo bad! *tear*!!
... But STOP STARTING SENTENCES WITH "BUT". Why not "This time I went alone because Michael is gone, and Susan hangs around different boys now, and Bridget is still crazy, and Carl's mom sent him to a Catholic school, and Dave with the awkward glasses moved away. That part, as cute and hypersensitive and weepy as it is, sucks. We never hear about these characters again. I was just kind of watching people, seeing who was in love and who was just hanging around, and I saw that kid I told you about. Remember Nothing? You mean from page 13? Whoa, I almost forgot, thanks for reminding me. -_- Nothing was there at the football game, and he was one of the few people who was not an adult that was actually watching the game. I mean really watching the game. He would yell things out.
...Now, normally I am very shy, but Nothing seemed like the kind of guy you could just walk up to at a football game even though you were three years younger and not popular.
"Hey, you're in my shop class!" He's a very friendly person. We know.
"I'm Charlie," I said, not too shyly.
"And I'm Patrick. And this is Sam." He pointed to a very pretty girl next to him. And, and she waved to me.
"Hey, Charlie." Sam had a very nice smile.
...Incidentally, Sam has brown hair and very very wtf pretty green eyes. HOW WAS ANY OF THAT INCIDENTAL. The kind of green that doesn't make a big deal about itself. I would have told you that sooner, but under the stadium lights, everything looked kind of washed out. It wasn't until we went to the Big Boy, and Sam and Patrick started to chain smoke that I got a good look at her. Yeah because two seniors in high school would totally just invite some geeky little wallflower crybaby loser to chain smoke with them after finding him alone at a football game.
"How old are you, Charlie?"
"Fifteen." And they looked at each other knowingly and drove away, right? Wrong.
"What do you want to do when you grow up?"
"I don't know just yet."
"What's your favorite band?"
"I think maybe the Smiths because I love their song 'Asleep', but I'm really not sure one way or the other because I don't know any other songs by them too well." I don't know why but I really hated the narrator right here.
"How about your favorite book?"
"This Side of Paradise by F. Scott Fitzgerald."
"Why?"
"Because it was the last one I read."
This made them laugh because they knew I meant it honestly, not show-off. I think "show-off" is a noun or a verb. Like, exclusively noun or verb. Yeah.

I feel ashamed, though, because that night, I had a weird dream. I was with Sam. And we were both naked. And her legs were spread over the sides of the couch. And I woke up. And I had never felt that good in my life. And I start all of my sentences with conjunctions. But I also felt bad because I saw her naked without her permission. I think that I should tell Sam about this ARE YOU KIDDING ME. and I really hope it does not prevent us from maybe making up inside jokes of our own.
...
And if that's not unbelievable enough,
Do you know what "masturbation" is? I think you probably do because you are older than me. But just in case, I will tell you. Masturbation is when you rub your genitals until you have an orgasm. Wow!
0_0
I'm only being cute here. I don't really mean it. I just wanted to make you smile. I meant the "wow" though. Yeah, that's cute Charlie. Adorable. WTF IS WRONG WITH YOU
I told Sam that I dreamt that she and I were naked on the sofa the second time I ever talked to her, and I started crying because I felt bad, and do you know what she did? She laughed. Not a mean laugh, either. A really nice, warm laugh. She said that she thought I was being cute.

Yeah, Chbosky obviously knows how the high school base operates. Because insider, beautiful senior girls think it's cute when scrawny emotionally disturbed freshmen have sex dreams about them and then tell them about it. This book just farted in my face.

So basically these two ultra-cool senior kids become Charlie's best friends for some reason. And he goes through drug experimentation, sexual experimentation (with, OMG SURPRISE, Sam the unattainable hottie), homosexuality and homophobia, abusive relationships, teen pregnancy, bullying, suicide, depression, social ostracizing, and so on. So basically every coming-of-age topic is covered in the span of a school year and Charlie talks about it in clumsy syntax with about 24,000 "ands" and 378,000 "verys". And even though it is a relatively harmless little book about some poor kid who is "just like you" in being deep and emotionally conflicted and tortured and very very very very special, it did absolutely nothing for me. The language and the story are both things we've heard before, but this reads especially badly because I've heard both things from MySpace. Or "The OC". Because

*SPOILER*

...as it turns out, all of Charlie's problems and all of his willingness to go with whatever cliched high school problem stems from, drumroll please, childhood sexual abuse. Ta-da. I'm sorry, but I couldn't help but roll my eyes. It's like... Charlie can't be a socially awkward cipher who cries easily, this childhood event between two people somehow explains every weird complexity in his personality. I've only taken 200-level Psych but I KNOW that one bad experience doesn't screw you over for eternity.

I heard a lot of good things about this book but the more I read, the more I felt like I was served an ice cream sundae but I kept finding hairs in it. Chbosky needs to learn that just because something sounds honest and has the occasional cute high school insight, doesn't mean that he shouldn't wear a hairnet. If that makes sense.

OSIDJFOASIDLKQWJEI I'LL NEVER GET THAT HOUR BACK.