Bands with no bad releases....

The only terrible Dream Theater album I've encountered so far is Octavarium

Even Octavarium had its occasional highlights (like the first track, and bits of the last one). Their disco rules, and WAID, if you don't like any of them, perhaps it's a matter of your taste and not their music making ability...? For their style of crazy ADD prog I think dt is damn near flawless

dying fetus has definitely had less than stellar releases
 
I think I'm gonna add Dismember to this list. I honestly don't think they've released anything bad.
 
I can't believe I forgot ayreon, because most of their discography is some of the best prog I've heard.

+ Pain Of Salvation
 
Opeth
Blind Guardian
Pagan Reign
Dream Theater
Symphony X
Nile
I wanna say In Flames and Shadows Fall because I love their older stuff so much but both band's past 2 albums were "meh"