Some fans have theorized that the final conversation between Tom and Summer in the park didn't actually happen - with the audio commentary suggesting that it could just be all in Tom's head. But the director and screenwriters disagree on this.
The narrative seems to view Tom as an immature Dogged Nice Guy who has an Entitled to Have You attitude. Tom admittedly does have an unhealthy view of Summer. The events in the movie is only shown from Tom's perspective and consequently we never get to know Summer as a person. Summer makes it clear that she's not looking for a serious relationship with him but he still throws a tantrum when his relationship with her inevitability falls apart. He never describes what parts of her personality he likes either, merely describing her physical appearance. At the same time, while Tom does overestimate some of Summer's actions, from his perspective she seems to give him little bits of false hope. It seems that Summer could possibly be aware of how much of a destructive presence she is in Tom's life and breaks up with him partly for this reason. It would explain her comparison of their relationship to that of Sid Vicious and Nancy Spungen, comparing herself to Sid.
Among fans of the movie, there is a clear divide between those who empathize with Summer and think Tom is an immature, selfish, delusional Yandere who unfairly projects the person he wants Summer to be onto her, versus those who empathize with Tom and think Summer is a selfish bitch. Interestingly, younger viewers tend to fall into the latter category, and many people say they empathized with Tom when they were teenagers and switched sides upon rewatching as an adult. Tom's actor Joseph Gordon-Levitt has made it pretty clear he's in the pro-Summer camp.
Big-Lipped Alligator Moment: The spontaneous dance sequence (the morning after Tom and Summer have sex for the first time), which is simultaneously a glorious movie musical dance scene and a hilarious parody of movie musical dance scenes.
Ensemble Dark Horse: Tom's little sister Rachel, played by Chloë Moretz, possibly the only person in the movie to realize that the Manic Pixie Dream Girl trope is not reality. Though ironically, as a child giving relationship advice to an adult, she herself is a person who doesn't exist in reality.
Fanon: Due to the Fourth Date Marriage some people have assumed that Summer met her husband while still seeing Tom - and thus broke up with him for this reason. Word of God has denied this.
Hollywood Homely: It's said earlier on how Summer is out of Tom's league, and a Jerkass at a bar reacts with shock at them dating. This is ignoring the fact that Tom is played by Joseph Gordon Levitt. He's dressed down in unflattering clothes and a slightly nerdy hairstyle but it still seems odd that Tom is supposed to be considered unattractive.
Jerkass Woobie: Tom's misunderstanding of Summer and their relationship is his fault; but it's never out of maliciousness, and he does genuinely care for her, and it's hard not to feel sorry for the guy. That being said, his Entitled to Have You attitude is shown as very damaging and a little dickish on his part.
Misaimed Fandom: Though he is a sympathetic character, Tom is being very childish in his expectations and is making some big mistakes, even if he's not doing it intentionally. Some people didn't pick up on this Aesop resulting in this trope.