I agree with what several people have said about FY -- it owned my soul at the time I was first watching it, and it's still a favorite, but I don't think it has worn as well. It's harder to rewatch all the way through without getting exasperated with the series' weaknesses. (Miaka may show up on my "most annoying anime character" nomination list later.)

I really need to bump Princess Tutu up higher on my watch list, so many people speak highly of it.