[kagami]

I don't think they are declining at all. You were...is a good example I think; a lot of people dislike it because they think it's boring/whatever but it is a visually stunning PV, packed with imagery and symbolism. And I think that's really the issue. Her PV's over the last couple of years have been more symbolic and abstract (aside from a few that have clear storylines). They don't clearly tell you what you're supposed to be feeling, and what you are seeing. You have to interpret it yourself.
MOON, to me, is like a painting. A painting that is dying. We get to see a picture in it's final moments. I can see how people think it is boring though, as not much happens.

As many people have said, she has fantasic and not so fantastic Pv's throughout her career. I don't think there is a particular era that outshines any other.