If you watch If, of course you must go on to watch O Lucky Man and Britannia Hospital, the second and final installments in Anderson's trilogy.
I've seen Bergman's Magic Flute several times, though not for years. In fact, I liked it so much the first time I saw it, I went back and saw it again the very next day. I remember being so exhilarated the first time that I walked home thirty or so blocks (I was living in NY at the time).
So, I liked it when I was eighteen. My mother, more musical than I, did not like it as much. But I think you'll find a great deal to enjoy: it's a very bright, childlike, charming movie. Sort of like a panto set to really good music.