Chinese Democracy comes to mind. Splinter does too. Ironically, Dexter Holland was considering naming Splinter "Chinese Democracy" because Axl Rose stole his dreadlocks hairstyle so he felt it was fit to steal his not-yet-recorded album name. Guess Chinese Democracy really does doom anything it's associated with.
St. Anger also disappointed the hell out of me and I haven't been able to look at Metallica the same since. It just goes to show that when rock musicians "get sober" their music tends to turn to shit. Hearing about James Hetfield's rehab and him trying to pass off "my lifestyle determines my deathstyle" and "frantic tick tock tick tock tick tock" as decent lyrics, the notoriously awful sound production, the trash can drums, the lack of guitar solos, ugh, just everything. I haven't even bothered to check out Death Magnetic. I just don't give a shit anymore.
Variety is a big one. It marks the end of Ringo's reign of flawless to nearly flawless albums. But don't take it from me - ask the rest of the EMF!