Well, for several mlp fans with good reasons, gentle and kind doesn't make him a good character. Pretty bland, a stereotypical pretty boy, the romance was too forced and kinda unnecessary, didn't anything important in the movie or episodes.
There are other who were butthurt that Flash stolen their "waifu".
To me, Flash is now at the "meh" side. He's not a bad character, but he isn't good either. Still, I kinda wish people would shut up about him.