This describes me, too. It all started with Lord of the Rings, then quickly spiraled into musical theater in general before narrowing down to Phantom and now, the Elisabeth musical.

I still have affection for the previous obsessions, and I doubt I'll ever "get over" them...I think there's nothing wrong with it, as long as you don't go overboard (and by that I mean, stalking people from that musical you're obsessing over, or something).