This is a spin off from the TVOTR thread really.
I find that when bands / artists take a nose dive in terms of quality, it makes me reconsider whether they were any good in the first place. Maybe it's that they become too stuck in 'safe mode' or maybe they can't recapture the excitement of their earlier work. It definitely seems to highlights tendencies and nuances that maybe didn't irk me before but now really really do.
Some examples include: Placebo, TVOTR, Bloc Party and NIN. All of whom started out with real promise and then went to shit, generally after album two.
Let's talk about it. Examples, reasons, etc welcome.