Everything by Blind Guardian except Nightfall - Never liked them, never will. Boring band by all accounts.
Amon Amarth - The Avenger - The only AA album I don't like and I can't explain why... it just didn't do it for me.
Angra - Aurora Consurgens - It was a big plunge in quality after Temple of Shadows. Still, some songs were good but overall nothing spectacular.
Cellador - Enter Deception - Too much hype for an average power metal album.
Nevermore - Dreaming Neon Black - I always hear people saying this is their best album while trashing Dead Heart In A Dead World. To me it's the opposite. I love DHIADW.
There's plenty more but I think that is enough.

Wait, when did people trash Dead Heart? That's actually one of Nevermore's most acclaimed albums. Enemies Of Reality is the album that takes the most heat (probably because it's less complex than other Nevermore albums).