Here's the next step. I added some layer filters, random brushing, and filled out some more color and definition of the walls and floors.
I feel things are looking better. But comments and suggestions are helpful.
NOTE: I have no idea how to make a grid in Photoshop. I'd like it to keep with the grungie, animated style I'm beginning to develop here. If someone knows how and would like to give me pointers, please leave me a comment or point me to a tutorial.