If I had to choose the nominee for the crappiest elevated stations in Queens, the Astoria Line (N, W trains) would get the designation. Not only do the stations lack artwork, but the windscreen walls do not even have any advertising on them, unless you count graffiti tags as unauthorized advertising. The Astoria Line has so much potential- remove the windscreen walls, and panoramic views of Manhattan are revealed.
Attached is an image of the Broadway station- no artworks, no billboards, no views. I've seen communist-designed stations that are more inviting and inspiring to the traveler.