Top of my list...
Evangelion: went from best to worst in only one episode

others of note:
Kiddy Grade (thought it was a "kiddy" show... lol then we had Eclair 0_0 *fwap fwap)
Gatekeepers 21 (nothing at all like it's predecesor. NOTHING...)
Guardian Hearts (reminded me of Kingdom Hearts and thought it too was a kids show. Then we had BIG CURVY naked women in the intro...

Papillion Rose (you GOT to see this to believe it. That title is SOO deceptive...)
any other anime you've seen with prejudgement that made you go
