This is fairly easy for me...two things. Not two bands, but two styles:
2) Most power-metal bands. Most of the songs sound entirely too much alike, and most of the bands sound entirely too much alike. I just don't see the appeal of a band if every song follows pretty much the same formula: Endless power chords in 4/4, break at totally predictable point for totally predictable solo, followed by somewhat catchy but oddly-familiar chorus, with endless double-bass drumming throughout. I just don't get it. I've actually listened to power metal bands at ProgPower, and honestly thought "didn't they already play this song?" Really.
Craig