It would probably make more sense for them to be evaluated in comparison to similar offerings withing the respective "genres" which would be hard for those that don't fit in to neatly defined formats, but it seems that most do.

I couldn't watch PewDiePie, it's damned irritating, but it's an entire format and style of video that some people like and he seems presumably to be the king of it and is widely emulated so it would be saying something then if you consider him overrated within that context. I couldn't venture an opinion though because I would just never watch that kind of video.