Behold, the major differences we noticed on "The Perks of Being a Wallflower" -- movie versus the book. Massive spoilers throughout!

1) The Entire Format

Book version: Every action beat is a letter, from Charlie, explaining what's happening.

Movie version: There are a few letters, but the action mostly plays out in a straightforward manner.

Level of Change: Moderate, as the book's method allows for a clear delineation of time.

Good or Bad Change: Good. Leaning too much on the voiceover would have made this film much cheesier.

2) The Older Brother

Book version: He's fairly prominently involved, from car rides during holidays to talking with Charlie about his girlfriend.

Movie version: He's still in there, but in much less of the action. He does have a prominent part near the end, but he's been largely cut from the first two acts.

Level of Change: Small.

Good or Bad Change: Understandable, given the constraints of running time.

3) Ponytail Derek

Book version: He's just the sister's boyfriend, no name given, though the ponytail is mentioned once.

Movie version: He's referred to as "Ponytail Derek," which is much funnier.

Level of Change: Moderate, because the "ponytail" emphasis seeks to humanize a fairly unlikable character.

Good or Bad Change: Good, because the movie needed some lightness at points.

4) The Introduction of "Nothing"

Book version: In the book version, Patrick has had his "nothing" nickname for quite a while.

Movie version: In the movie, his shop teacher bestows it upon him.

Level of Change: Small.

Good or Bad Change: Good. They didn't have the room for the back-story, and this is an elegant and efficient way to handle the change.

5) Charlie Gets a C

Book version: On his first essay, his English teacher, Bill, gives him a C for prominent use of run-on sentences.

Movie version: In the movie the English teacher has a last name, Mr. Anderson (Paud Rudd), and he's pretty much effusive in his praise.

Level of Change: Moderate, as the essay grading shows Charlie's progress as a writer, and in the organization factor of his mind.

Good or Bad Change: Decent, because the teacher was another character they couldn't fully explore in the film, given they didn't have 256 minutes to work with (the average written page equaling a rough minute of screen time).

6) Aunt Helen Was Corpulent?

Book version: Charlie mentions Aunt Helen's size so he can effectively use a vocabulary word the English teacher wants him to use.

Movie version: Movie version Aunt Helen is played by Melanie Lynskey, who is normal Hollywood size (small).

Level of Change: Moderate.

Good or Bad Change: I'll go with slightly bad, as it wouldn't have hurt to go with accuracy here. But this could be a quibble over definitions, as perhaps in the writer's mind the actor portrayed the character exactly as he'd intended.

7) The Last Episode of 'M.A.S.H.'

Book version: The family watches the last episode of "M.A.S.H." together, and the father cries.

Movie version: Doesn't happen.

Level of Change: Moderate.

Good or Bad Change: Charlie's father was another cut for time, but this could have been a quick two-minute scene.

8) Patrick's Speech About Women

Book version: In the book, Patrick has some advice for Charlie about how to treat a lady.

Movie version: Patrick provides counsel, but nothing too specific.

Level of Change: Small.

Good or Bad Change: Good. Patrick gets plenty of screen time already, and his little speech might have made some female audience members roll their eyes.

9) Michael's Passing

Book version: The book gets right out in front of it, Charlie's friend killed himself.

Movie version: This information is held until the critical "first party," when Sam (Emily Watson) is making Charlie a milkshake as he's stoned. The book version doesn't have this reveal to Sam, though Charlie is still "toasted" by Patrick afterward.

Level of Change: Big.

Good or Bad Change: Good, even though this changes the narrative tension. In the book, it's placed up front, to get you invested right off the bat. In the movie, the cards are held a little closer to the vest, though it helps in a big way with the Sam / Charlie relationship.

10) Charlie's Dad Hits Him

Book version: In the book, Charlie "hurts" Aunt Helen's feelings, so his dad smacks him, which causes Aunt Helen to come to his aid.

Movie version: Doesn't happen.

Level of Change: Moderate, as this immediately sets off a few red flags.

Good or Bad Change: Good, though again in service of the third act of the film. The Aunt Helen reveal is pretty jarring, mostly because the film hints at it much less than in the book.

Book version: Charlie hurts a kid named Sean in self-defense.

Movie version: Charlie doesn't seem prone to violence prior to the huge Brad vs. Patrick fight.

Level of Change: Big.

Good or Bad Change: Good and bad. Good because it makes standing up for Patrick into a huge deal. But bad because the "violence" issue in the book shows that Charlie is struggling, from the outset, much more than it seems in the film version.

12) "We Accept the Love We Think We Deserve"

Book version: The English teacher says this in both, but in the book Charlie reveals his sister was hit by her boyfriend.

Movie version: Doesn't happen.

Level of Change: Large.

Good or Bad Change: A good change for time, as it avoid the whole Ponytail Derek saga, but we again lose some prominent action.

13) Charlie Witnesses Oral Sex

Book version: As a kid, Charlie's older brother throws a party in the house, and Dave sexually assaults a girl.

Movie version: Doesn't occur.

Level of Change: Massive.

Good or Bad Change: Understandable, given the need for dramatic arc. This would have been another huge red flag as victims of sexual abuse are far less likely to report sexual abuse. If this had been in the opening half of the film, audiences would have been wary of what was going to be revealed next.

14) "Landslide" vs. "We Can Be Heroes"

Book version: "Landslide" is the song played as Sam does her "standing up in the tunnel" routine.

Movie version: "We Can Be Heroes" is the song.

Level of Change: Huge, they are far different songs in terms of tone.

Good or Bad Change: The book is more melancholy, the film is more whimsical. Tough to judge which is better, just depends on your mood.

15) Aunt Helen Gets Beaten By Grandpa

Book version: Aunt Helen is a victim of physical abuse in her childhood.

Movie version: There's very little Aunt Helen backstory, she mostly appears as a vision.

Level of Change: Big, as this would have (again) tipped an audience off as to where we were headed. Victims of abuse are more likely to become perpetrators of abuse.

Good or Bad Change: Good, as the third act reveal strengthens the picture.

16) Bob Says "Too Much" About the Gift

Book version: In the book, Bob receives the bubbles from Charlie for Christmas, stating the above.

Movie version: In the movie he says something to the effect of "He really knows me."

Level of Change: Small.

Good or Bad Change: Good. Better language, which gives the audience the impression that Charlie is a person who values other people.

17) The Abortion.

Book version: The abusive boyfriend gets Charlie's sister pregnant, and Charlie drives her to a clinic. She then breaks up with the boyfriend for good.

Movie version: None of the above transpires.

Level of Change: Big, because it allows for connection between Charlie and his sister.

Good or Bad Change: There probably wasn't a great way to get this much of the sister in the film, but this edit still feels like a bad one, because it's fairly critical to the sibling relationship.

18) Charlie Develops a Smoking Habit

Book version: After he's ostracized, Charlie starts smoking heavily.

Movie version: He smokes, but there doesn't seem to be an emphasis on it.

Level of Change: Small, though a smoking teen is different from movie Charlie.

Good or Bad Change: Fine, as they couldn't set up the "hero" as a smoker given the current MPAA feelings on smoking. They would have been risking an R rating.

19) The Emphasis on Driving

Book version: Charlie really wants his license, and takes a driver's ed course.

Movie version: Doesn't happen.

Level of Change: Small.

Good or Bad Change: Good, another cut for time.

20) The Brad vs. Patrick Fight

Book version: In the book, Charlie wins the fight and then threatens to expose or blind Brad the next time.

Movie version: He doesn't threaten to tell, and he doesn't really remember anything.

Level of Change: Big, because it makes Charlie an active fighter as opposed to a "put upon" guy who happens to win fights.

Good or Bad Change: Bad. I like fighter Charlie better, as it's a more interesting character.

21) Patrick Quits "Rocky Horror Picture Show"

Book version: Patrick quits the main part in the show after his fight with Brad.

Movie version: Never happens.

Level of Change: Small.

Good or Bad Change: Good. This shows Patrick's overall depression, but the film shows that just as effectively.

22) Brad "Cheats" on Patrick

Book version: During Charlie and Patrick's drinking binge, Brad is spotted with a man.

Movie version: Doesn't exist.

Level of Change: Medium, because it shows that Brad is struggling with his sexuality just as much as Patrick is struggling with Brad's family situation.

Good or Bad Change: Bad. It would have taken 20 seconds, and would have made Brad a more sympathetic character.

Book version: In the book, the seniors fill a swimming pool with grape Kool-Aid.

Movie version: In the movie, Patrick turns all the shop instruments pink.

Level of Change: Small.

Good or Bad Change: Good. Anytime you can get a main character more involved in a comic way, you're winning.

24) Sam's Penn St. Yearning

Book version: Doesn't exist.

Movie version: Sam often mentions she wants to go, and Charlie helps her study.

Level of Change: Small.

Good or Bad Change: Good, as it brings Sam and Charlie closer together.

25) Craig Switches the Music

Book version: At the graduation party, Charlie deejays, does a good job, plays happy music when people are down.

Movie version: Charlie's mixes are too sad, Craig puts on something happy, says something derisive to Charlie.

Level of Change: Medium, as it sets Craig up as a jerk, as opposed to just a guy.

Good or Bad Change: Bad, because we're now in an arc that goes pretty dark in the film. Movie Charlie struggles over the last half an hour, all the make the last big reveal tonally correct, where book Charlie has a more layered existence.

26) Charlie and The English Teacher Meet

Book version: Charlie meets Bill (not Mr. Anderson) for lunch at Bill's house, where they have a heart-to-heart about how gifted Charlie is.

Movie version: Never happens.

Level of Change: Large, because it makes the English teacher into more than a bit part.

Good or Bad Change: Bad. As a reader, it's nice to see adults take an active interest in Charlie, whereas in the movie version it doesn't really happen until Dr. Burton (Joan Cusack) is involved.

27) The English Class Bully

Book version: Doesn't exist.

Movie version: The same girl always calls Charlie names in English class. She's a real gem.

Level of Change: Small.

Good or Bad Change: The rare movie "addition," this one was likely put in to hammer home that Charlie is an outcast among his peers.

28) Charlie Realizes About "Aunt Helen" While With Sam

Book version: Sam and Charlie begin to get physical, which triggers an awful memory.

Movie version: Charlie "remembers" while in the psychiatric ward.

Level of Change: Big.

Good or Bad Change: Good. The film couldn't risk the negative association with Sam, so they just went with Charlie freaking out, calling his sister, and then figuring everything out. Understandable.

29) The Aunt Helen Wrap-Up

Book version: Charlie tries to come to grips with why Aunt Helen did what she did, and why people are the way they are.

Movie version: No real afterword on the Aunt Helen plot line.

Level of Change: Moderate.

Good or Bad Change: Neither, just a signature difference in the written word vs. the visual medium. Though the omission of point #15 made this the de facto route to go for the film. Otherwise things would have gotten too muddled in the narrative.

30) No Mention of the Final Song

Book version: Charlie stands in the tunnel, but no song title is given.

Movie version: They solve the mystery of what song they liked, and that song was "We Can Be Heroes" by David Bowie.

Level of Change: Medium.

Good or Bad Change: Good. It helps to have a song to identify the film with, and to provide momentum for the final scenes.

There you have it. All in all, a pretty remarkable adaptation from writer / director Stephen Chbosky. As this list is by no means definitive, feel free to add your own in the comments section below!