Probably just echoing what others have said at greater length, but I
remember in high school and college not caring much for Mozart's music. I
knew only a few pieces but their true worth escaped me at the time. I was
much more bowled over by Beethoven. Haydn, from the little I heard (e.g.
Beecham's recordings) I found quite witty and full of surprises. Mozart's
music seemed bland and seamless. I can't recall exactly when it "hit" me
but it did. Until one picks up on the subtleties of his mature works (at
least from K. 271 on), one can't really be blamed for not appreciating
them. Time doesn't permit citing examples here, unfortunately. It was
just as he himself said: entertaining on the surface but paying more
rewards the deeper you dig.
Chris Bonds