[Jeritron]

I don't think Gambit is "overrated." I think he's just a great supporting character who caught on very quickly and became way popular among fans because of how "badass" he was.
What his character represents and brings to the table doesn't really match that popularity. He just doesn't have the substance, (from what I've read) to match his style.

So basically what you have is a character that isn't tremendously deep, nor should it be, but their popularity has brought them to a level where people either pedestal them, or resent them for not being as realized as a Joker or Magneto. Supporting characters with the popularity of major players.

This happens all the time with pop characters, though. It's the Boba Fett effect. I can't say anything because I love Gambit (and Fett), but it's almost definitely a style thing.