I keep seeing that a lot of people expected an idea like this to not work at all, but for me, it's not surprising at all that a group like this has gathered this much attention. And that might be part of my main gripe with it. It just feels like this group was conceived after careful analysis of the demographic they intended to cater towards. I'll listen to one of their albums and while it's mildly enjoyable for what's its worth (that is, in the same way a disaster film is enjoyable for what it's worth), it just doesn't come off as sincere. I imagine that a team of executives wrote off on paper what they knew would make a big splash in the Japanese music scene, and to give them credit they definitely succeeded.
As far the music goes, it's fun but after a while becomes rather derivative and soon after, a bit of a one-note shtick. While the blending of genres here is new, in execution it isn't as strange or weird as a lot of people are making it out to be. I mostly just hear by-the-numbers thrash and power metal riffs with J-pop vocals added on top while most of the songs are structured the way a pop song would be. In the way of genre-blending, it's really not all that interesting or engaging. I can see some people liking them, and they're not exactly horrible, but they're definitely not something I would return to.