I dunno. I don't think X2 was really as great as people make it out to be. I mean, I know it's like pissing in the wind trying to convince people it's not the best Xmen movie, but yeah. I think First Class is the best.
I actually think Singer stunned the world so much when he made X-Men, and people were so stunned that it wasn't terrible, that he got TONS of love. That whole "Pretty okay quality" superhero movie, at the time, was a huge win for Hollywood. This was before Raimi came and blew the doors off with Spidey, and long before Nolan turned the whole thing on it's head with Batman Begins. Singer got so much love, and then he did another "pretty okay" job with X2, that it is still carrying him today. If I told you the guy who made Superman Returns and
James the Giant Whatever was making Days of Future Past, there would not be this long of a thread about it.
Plus I'm convinced that the only people who didn't like First Class are people who have an erotic fascination with that guy from Swordfish.