Okay, I'm a fantasy fan. I cut my teeth on Merritt as a teen but caught up on writers like L'Engle as an adult. Personally, I think she had a lot to say about the nature of love. Regardless of your age, there's something to be learned even on the second or third reading. L'Engle, like most great children's authors, is deceptively simple.
As for her importance, the half page obit in the New York Times blew my mind. Someone else must agree with me about her importance.
PS: Must say I liked the Murray books better than the Austin books. Must be something about cooking dinner on a bunsen burner.