Now, this is rather weird, given how profoundly embedded I've been in fantasy and science fiction since about 4th grade. I never had any problem accepting hobbits, or lensmen, or what have you. I think the distinction is that I've always been very text-oriented (I literally can't remember not being able to read), whereas I'm virtually blind to the nuances of music, and deeply inept at pretty much any form of dance which doesn't involve St. Vitus.
It has been in raising the_child, and being an active participant in her movie watching -- something her mother and I have always carefully monitored and managed -- that I've come to appreciate the musical as a story-telling form. Many of the movies I yawned through or scorned in my youth have acquired a vast new power for me. Mary Poppins can be seen as a radical deconstruction of Mr. Banks' life, with strong feminist and post-modern tropes rather ahead of their time. The Music Man is downright dirty, in a very funny way. Chitty Chitty Bang Bang is a rather clever exercise in frame making and breaking, as well as a bizarre fusion of Charlie and the Chocolate Factory and the James Bond ur-story.
It makes me wonder what else I've missed in my dismissal of literary and artistic forms. We all have our tastes, developed in different ways. What have you come back to later in life that you might have rejected at first?