Rhythm games could've stood a chance if they didn't milk the consumer for every penny they had. They should've stopped with guitar and vocals.Harmonix games are pretty shitty.
Their best game was Guitar Hero 2, but then again, Guitar Hero 3 was a lot better and ironically not developed by a company that solely makes music games. The pro guitar mode in Rock Band 3 where you could supposedly learn how to play guitar for real was a total joke, while Rocksmith actually did that concept right. And their multi-track music games like Frequency and Amplitude were kinda terrible, I couldn't ever get into the flow of the song when you have to abruptly switch patterns every few measures.
They're not very good at making tough charts in Rock Band, either. Difficult charts can be fun when they're well made, but I really can't think of a good one of theirs.
Just Dance for instance. After 3, they could've just done music packs instead of releasing it yearly. It works better as a platform than a yearly franchise.
Guitar Hero 3 was peak Guitar Hero. After that, it was just disc expansions.