Idea - How strong and original is the concept? Is it a good response to the contest topic?
Technique - How well executed is the background as a piece of art within the chosen style?
Usefulness - How well would it work as an adventure game background, and how useful would the background be in a game?
Since I didn't have time to join, I'll at least take a few minutes to vote:
Idea -
Questionable - Because it depicts a scene in the same world that is at a completely different location than the original.
Technique -
Mad - Since each of the pieces has another artists' 'chosen style', I've chosen Mad's piece for this category, since it best reflects the original artist. I think it fits well within a single game with the original/inspirational piece...without people seeing different styles. And that's not a small feat.
Usefulness -
Questionable - I could immediately see some interaction-points in this interior-scene. While I think the other pieces can also work, these interaction-points give a clear purpose to the room (or at least a wish to investigate it). In this regard, the piece from TheRoger suffers from the fact that the inspirational piece by nihilyst felt more like a title-screen than an in-game screen...and while I can clearly envision nihilist's piece with the title scrolling to the right (into TheRoger's piece) and settling while a mysterious wanderer walks in from behind on his journey, it still feels a little stuck to the title.
Some additional comments (I hope they don't sound too negative, because they're not intended as such):
- Questionable: When I looked at the original piece by Pinback, I would have expected the rooms to be narrow and high, and very Victorian inspired; like the image below (click for a bigger version). Instead you've created a low-wide room.

If you look - for example - at the windows in both pieces you see an entirely different architectural style/era. This difference - even more than the drawing style - make these pieces not fit within the same world.
- TheRoger: Somehow the piece feels a bit repetitive of the original (particularly due to the shape of the mountains). Taking the scrolling-movement I described above into account, with the main character starting/on his journey, I would have liked to have seen some sort of fantasy (Buddhist-inspired) temple to the right that creates both a starting-point for the story and serves as an initial description of the main characters.

- Mad: What I miss most is a clear exit - like a cavern or something - on the left. It's a little difficult to envision exactly how it would look in this semi-silhouette-style Ben choose for his piece; maybe adding an animated torch that chances colour from yellow (good) to blue (evil), and settles depending on the player's choices might be helpful to lead the player's eye. Also, to me the little flame by the sign doesn't seem to fit (within Ben's story for the original piece).
Edit: Changed some of the wording regarding Mad's piece.