They are largely boring and bland. They sound like a 5th generation watered-down version of a mid-tempo grunge band. Like many people who don't care for them, I only know very few of their songs. What about them would make me want to dig deeper? I mean, the lyrcis for Photograph are bad.
Obviously some people like them. And honestly, good on them for all that hard work early on. I respect that, but not their music. And there is nothing wrong with a little snark thrown towards them and their fans. It's just music, after all. There is room for some criticism, and that's inevitable with the amount of music they've sold.