I always thought the hate is because Gambit is simply too cool. Neat powers that he uses in his trademark way, sexy accent, master thief, lady killer who wears a trench coat.
It's a bit much
All of this also happens to give him a tremendous amount of potential as a movie lead.
While he has been taken down quite a few pegs in recent years, his too cool-ness is why I've always felt he works better as a solo character than as part of an ensemble cast.
I always point to the first half of Gambit's '99 solo series as the best showcase of what makes the character work. I'll shill it forever. It balanced the elements of his character in a way that made him more nuanced and believable while still maintaining the inherent coolness. It was also drawn by the guy that did the storyboards for The Matrix, so the action scenes were top notch. The second half of the series had much worse art, but was still pretty good even though it got a bit off the rails weird.
It's also worth mentioning this book was selling well and then got cancelled for no real reason other than Joe Quesada wanting to trim down the X-Men line. It marked the beginning of Gambit's decline in relevance in the comics.
