Here's my list:
Nine Inch Nails - With Teeth/Year Zero
I was a die hard NIN fan back in the day and when With Teeth was released, I was psyched. I have not heard anything new from them since The Fragile and I just had to get my hands on it... and then I listened to it. With Teeth is not a bad album but it was a major disappointment compared to the early days. When Year Zero came out I gave up completely on NIN and came to the conclusion that Trent stopped doing anything that interests me. Music with a political agenda can work if there's some actual deep thought put into it. When it's just a series of shallow, barely satirical cheap shots at everything the lyricist hates, you can kind of tell the difference. Now that Trent has gotten over hating himself, his anger toward the rest of the world has nothing to balance it out.
Rush - Caress of Steel
As I have admitted many times, I am a Rush fanatic... but Caress of Steel was a major disappointment for me. Compared to their other albums, this was a snooze fest with the exception of Bastille Day and Lakeside Park. Thank goodness 2112 came out the next year to liven things up.
Rammstein - Rosenrot
The previous Rammstein albums did not fail to amuse me... until Rosenrot was released. This album lacked the edge from their previous albums that made them so incredible and entertaining. I was so bored of this album that I can't even remember what the tracks sounded like. I just remember the dull feeling in the pit of my stomach listening to it.
Captain Beefheart and His Magic Band - Strictly Personal
Beefheart's debut Safe as Milk was an incredibly solid musical treasure to the ears. Strictly Personal was the second album and like I have mentioned in the last two entries, it was a bore fest. Nothing on this album really stands out with the exception of the song Safe as Milk (which was not originally released on the album it shares the same title with.) The lackluster production is a major factor. Say what you want about Trout Mask Replica but at least that album had some substance that kept things lively. There is none of that on Strictly Personal. Even Don was disappointed in how the album turned out. When even the guy who made the album considers it a let down, you know you're talking about something bad.
... and that's all that I can think of off the top of my head. If I can think of any more, I'll be sure to add it to this list.