First example that comes to mind is Opeth. Everyone I know is or was raving about Opeth, and I couldn't dig a song for the life of me. I don't like extreme metal with harsh vocals, ok, there are the more clean vocals songs... don't like them. They also made an acoustic album, cool.... I found it boring. I just have to accept that Opeth's music is not meant for me.
Also a lot of prog stuff here and there doesn't really captivate me too much. The point is that I don't listen to Dream Theater because I like prog, Dream Theater is the only reason why I even bother to check out other similar bands of the genre here and there. For example I tried giving a shot at Transatlantic but even though there's nothing I really dislike, as in "Bleah, what is this, I don't want to listen to it anymore", nothing really stands out to me (We All Need Some Light is cool though).