I'm actually quite good with terrain, but I can't do over detailed things, like a canyon...
Interiors I just suck at. Sometimes I get lucky and make something good, but it's rare.
I never made a floating island. I better see how well I can do with that.
Caverns are far out of my skill range, but I have tried though...
Houses aren't too tough to do, it's just the interiors that get me.
I recently discovered my ability to make a pink leafed Japanese tree. They are time consuming, but well worth it in the end.
You should add a TDM/DM option to the poll. Many people love doing those.