Eddy's Brother: Was he always a brutal bully to Eddy or did the abuse only start at a later point in his life? Episodes like "Ed, Pass It On" strongly suggest the former, yet several of his Pet the Dog moments throughout the series (teaching Eddy how to make the El Mongo Stink Bomb, promising to give him his car when he turned 14, trusting him with his Porn Stash) point to the latter interpretation.
Eddy: There are several interpretations as to why Eddy chose to seek help from the one person who had been tormenting him for most of his life:
Given how much Eddy still brags about his brother, he could have a warped view of their relationship and genuinely believe his brother would be willing to help.
The movie also retroactively gave this to Eddy's parents, who were thought to be as neglectful as Ed's, given that it's reasonable they may have given him tough love so as to not end up like his brother. Eddy after all was scamming kids. Not to mention, he has a Number 1 Son mug in his room and his brother checks to see if their parents are around, indicating they're protective towards Eddy against his wrath.
Arc Fatigue: A majority of the film covers the kids journeying from the cul-de-sac to Eddy's Brother's house, with next to no actual plot development. Almost everything between leaving the cul-de-sac and arriving at Eddy's Brother's house could be cut out of the film and very little would be lost. If anything, it would just be a half hour episode.
Ass Pull: Eddy's brother's sociopathic nature was foreshadowed a few times in the original show - most of all in "An Ed is Born" ("No more beatin' up little Eddy, hey, big brother?"), but the ending feels like this to some. All of the damage Eddy took was all of a sudden Played for Drama, and the kids instantly forgive and befriend the Eds afterwards.
Author's Saving Throw: The movie addresses a few complaints about the show: Kevin and Sarah getting hit by karma, Kankers helping the Eds for once, Eddy apologizing for his actions, and the Eds becoming accepted by the community.
After learning that Eddy's Brother was a cruel Jerkass who tormented Eddy for most of his life and lead to him becoming a scamming Jerkass, watching him get hit with the door of his own trailer is worth a cheer or two.
Cargo Ship: Kevin got shipped with his bike a lot thanks to the movie, where it's an entire plot point that he cares more about it than Nazz, much to her fury.
Yes, the Eds have been accepted by the kids at the end of the movie, but they'll still probably be in trouble for the collateral damage caused by "The Scam that Went Too Far" (which includes a broken water pipe, an uprooted tree, two damaged back yards, and a house filled with cement).
Although everything is shown to be perfectly fine in the ending cutscene where Johnny uses a telescope to overlook the neighborhood. The Eds and the kids probably may have used ToonPhysics to fix everything.
Unless it's declared non-canon, "Take This Ed and Shove It" completely overrides this film's happy ending, as the elderly members of the cul-de-sac treat the Eds with as much disdain as they usually did.
"Take This Ed and Shove It" actually is non-canon, as the future shown in that episode was simply a bad dream that Eddy was having. At the end of that episode, where Eddy wishes he were a kid again, the other cul-de-sac kids aren't shown, so they're probably still friends with the Eds, but just not living close to them anymore. As we see the Eds in Eddy's room, it's possible that Eddy either didn't get his own place all those years or moved back in at an older age, with Ed and Edd either visiting or being his roommates, and Eddy wishing he were a kid again could be him being nostalgic for the good times he had with the other kids in the events after the movie.
Regardless, none of the seniors are shown to be in the right state of mind, as is sadly all too common for the elderly, is memories and attitudes are likely distorted.
Misaimed Fandom: Some viewers (with quite the shallow hatred of Eddy) enjoyed Eddy getting beaten by his abusive brother because of the quicksand prank, ignoring that Eddy had already suffered and learned from that experience. Others at least decided when Eddy's had enough and thought his brother eventually went too far.
Moral Event Horizon: Eddy's Brother crosses it when he begins to hurt Eddy for no other reason but his own sadistic pleasure, and then admits freely that he's always done this to him in his whole life.
Narm: Eddy's sobbing during the scene where Double D briefly leaves him and Ed can slightly come across as sounding a little ridiculous and unintentionally faked, just listen to it.
One-Scene Wonder: Eddy's brother only appears in the last five minutes of the movie, yet leaves a huge impression.
Signature Scene: The quicksand prank, Edd and Eddy's ensuing fight, and Eddy's brutal beatdown at the hands of his brother.
Some Anvils Need to Be Dropped: The characters each learn an important lesson along the way and theyre well-executed despite being told with the subtlety of a jackhammer.
Ed: Even if you may not know it, youre much smarter than you or others believe yourself to be. All you have to do is put your mind to it.
Double D: Standing up for yourself is important and if you dont, you wont be true to yourself.
Eddy: If you do something really bad to your friend (in Eddys case, tricking Double D into thinking he and Ed drowned to death), you could lose them permanently and the hurt probably wont go away.
All of the Ed Boys: You dont have to live up to any expectations or legacies for people to like you. Accept yourself for who you truly are.
The kids: If revenge is all you think about, it will make you no better than the person who wronged you.
No matter how many times a person has wronged you, maybe all they really need is a friend.
Sometimes, your biological family is just plain awful and youre better off without them, but that doesnt mean you wont have one. Eds parents dont seem to care much about him and give Sarah everything and Edds parents barely pay attention to him or consult him. However, Eddys brother is supposedly much better than his parents, but it turns out hes a cruel and absuive jackass who made Eddy the way that he was. In the end, Eddy admits to all his faults and begins to see that his friends are his real family.
Squick: Rolf milking a cow and then drinking the milk...without filtering the milk.
Eddy. After learning that his brother is an abusive jerkass who frequently beat the living daylights out of him, prompting him to create a Jerkass facade as a desperate attempt to make friends - then recounting various episodes where Eddy is punished and humiliated... who knows what would have become of him were it not for Ed and Double D's companionship?
Edd, after the quicksand prank. Especially with his reaction when he believes both his friends are dead, he seems truly broken. He even said he was thinking he had lost "the only two people I have left in this world".
Jonny. The ending of the movie was happy and heartwarming for everyone...except for Jonny, who is beaten up by the kids, left without friends, and even turns evil. All because of a misunderstanding.