Just shut up, he does not suck. His vocals have infinitely more personality than most metalcore screamers. With metalcore, the vocalists look and sound like they feel obligated to scream rather than doing it because they want to. (see: Triviums "Pull Harder on The Strings of Your Matyr" And at least we know he doesn't use effects. That has to be the lowest thing a metal vocalist can do.
As for Celine Dion, I don't like pop in general. She may be a good singer, but it's not my thing.