Even going through all my favorite bands, Meshuggah, Nevermore, Opeth, Pantera, Megadeth, Candlemass, Darkane, Behemoth, Atheist, etc., I can't name even one band that has never disappointed me. They've all put out a disappointing album once or twice.
By disappointing i don't mean bad at all(with exception of megadeth, because pretty-much everything they made in the '90s sucked), I just mean disappointing. Albums that weren't as good as I'd come to expect from them, though if put out by a different band I'd think were pretty good.
I've got nothin', but maybe I'm just too critical of my music.