I feel like most people have said it already, but Boku no Pico. That was the joke of the community about 10 years ago and it left everyone traumatized (I still remember being told "New to anime? You should watch it, it's great!").
I've also been disappointed by a ton of recent animes due to the new 3D CG that they've been using (*cough cough* Bers...... 1 reply
