Incredibly zany powers and excessively bright colors, the entire Capcom side, magic series-style combos, combos that are inherently flashy and last long periods of time, other general airdasher mechanics, and I'm sure the list could go on.
From what I see, Marvel games have everything your typical "anime" game has, but takes it to broken, yet fun extremes. It just tends to avoid an anime stigma because it's A) a Capcom game, and B) half filled with American-style characters and half filled with characters from (generally) loved Capcom games.