Well, if werent for Opeth, I wouldnt be here. They brought me into metal and pretty much began my musical metamorphosis. They are still one of my favorite bands, but I dont listen to them quite as much. This band got me into everything that is metal.
Agalloch totally changed my view of music. Not so much from their music, (it is incredible) but from what and who they were influenced by and into in interviews. I mean, I grew fascinated with this band (still very much am) and I thought Wow, they like a lot of music other than metal, perhaps I should check it out. I then checked out all these bands they were raving about and, needless to say, my musical horizons have broadened substantially. Ive said here before that Im listening to a lot less metal nowadays, and its thanks to this band. Im not sure if its a good or bad thing; it is what it is. The band also allowed me to like more minimalist styles (whereas prior I wanted everything to be technically proficient). I am much happier listening to things because I actually like it with out my mind being clouded with this notion that music must be technical.
Ulver has totally rearranged my view of electronic music. Before I hated it and I never even gave it a shot, but now I am now very much into the darker styles of ambient and electronic music.
Atmosphere introduced me to (underground) hip-hop. It actually conveys meaning in the words and the music is pretty cool too. Im not huge into hip-hop at this moment, but Im still looking into it.
Musical tastes should always be evolving (as everything else in life). It keeps things interesting and vigorous.