Exactly this for me too. I spent much of my teens listening exclusively to three or for bands and dissing any other music and anyone who didn't share my tastes! Now, realising what a bleedin' idiot I'd been, I listen to anything or everything with what I hope is a reasonably open mind. I am still occasionally smitten, as in I know within a few bars that I'm going to really dig something but if something doesn't hit me like that I will still give it a few whirls and see if it grows on me.
The opposite for me, some bands I have to finally admit I do like them!