If you had asked me, in my early twenties, what makes people "cool", I would have put "what music they listen to" somewhere near the top. In fact, if you had asked me to name one thing that was wrong in the relationship with my then-girlfriend, I would have said "musical incompatibility."
Now, eight years (or however long) into my current marriage, I can't believe I used to be so petty. Actually, I'm pretty sure that the difference between bad and good music is largely semantic. Wendy was game when we first started out, eagerly subjecting herself to the bands I foisted on her (and, I like to think, she had a few things to teach me as well), but if she hadn't even been willing to act interested, I wonder how long I would've bothered.
I guess the issue wasn't that I wanted someone who liked all the same music as me, I just wanted someone who was open to trying out new sounds, even having new experiences. That IS something important to find in a relationship, at least for me.
That's my thing that I used to judge people too harshly for, that I now know doesn't matter. What's yours?