Penetration.
Can't say that that's what I listen for as much as it is what I hope to feel.
Make all the jokes you want, but that's what I'm after - a meaningful penetration into my world. I have a world, thank you, and I can't say that it's particularly empty, at least not so empty that I'm willing to let anything and everything into it "just because". You gotta give me something I can USE.
The quickest routes to getting in the door are usually through tone (individually or collectively) and rhythmic substance (which only sometimes comes in the form of a "groove"). Those are both qualities having to do with the vibrational, and it's the vibrational that penetrates the walls/barriers/etc. Once the barriers are broken, we can negotiate what, if any, meaning the experience will have (or can possibly have), but without that initial penetration, it's like water off a duck's back.
The older I get, the more water there's getting to be, but I ain't dead yet.