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.
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.
Ass Pull: Eddy's brother's sociopathic nature was foreshadowed a few times in the original show, 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.
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.
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 Façade 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.