** A fairly minor one, but the revelation that Mr. Buu [[spoiler: created a wife named Buuby and went on to have kids with her by shooting her with a "love beam"]] is either hilarious or idiotic depending on who you ask.
** The game itself. Those who know about it debate its canon status as frequently as they do ''[=GT=]''. Specific elements of contention include the prevalence of the Super Saiyan transformation, and New Namek and Yardrat's destruction. This has only been exasperated with the release of the Xenoverse games, which uses the characters, setting, and plot points of Online but in a different context, muddying the waters further.
** All Human players actually being saiyan hybrids descended from Goku or Vegeta is also one. Particularly for players who wanted to play as actual Humans without alien lineage or didn't want to be [[HeroicLineage descended from]] Goku or Vegeta ( WordOfGod however has established that pure humans are still the weakest race, so the decision is justified somewhat).
* CharacterTiers: Namekian Shadow Knights in particular were considered the best PVP class. Other High Tier classes were Swordsman and Dende Priest for PVE. On the lower end, Turtle Hermit wasn't considered that useful, and inferior to Crane Hermit in most aspects.
* EnsembleDarkHorse: The Majin race was the best received idea of the game, to the point they even made it into Dragon Ball Heroes!
* FridgeHorror: We know that a PowerLevel of 18,000 is more than enough to casually destroy a planet. The average player's power? 100,000. Any nut with some spare time could easily blast the Earth's core wide open in an instant.
* NeverLiveItDown: Fitting that [[JokeCharacter the weakest class in the game]] is the one founded by [[TheChewToy Krillin]].
* ScrewedByTheNetwork: The developers did know that there was an English audience - [[MoneyDearBoy the costume store even accepted US dollars]] - but that still didn't stop them from shutting it down due to a perceived lack of interest.
* SurprisinglyImprovedSequel: Several plot elements are considered to be a better then the equivalents in ''Dragon Ball GT'' by fans. It helps that Goku and Vegeta presumably met their end in a blaze of glory befitting two Saiyan warriors rather than [[GainaxEnding whatever that was]] at the end of GT.
* [[TheyWastedAPerfectlyGoodPlot They Wasted A Perfectly Good... Everything]]: The game was shut down before a lot of elements could have been expanded on. The Mechanic classes, Cell's clones and descendants, [[BigBad Miira]]'s plans, all those had merely passing mentions before the end. That's to say nothing of the character creation system, which after the shutdown left only the generally-loathed ''[[VideoGame/DragonBallZBudokaiTenkaichi Ultimate Tenkaichi]]'' as an option for those with AltItis.
** It seems that the people making VideoGame/DragonballXenoverse are looking to subvert this, what with the superior character creation as well as the recycling of several characters and plot elements from Dragon Ball Online.