As you mentioned already shadows are one of the best things to add to give a sense of depth. With your bevels consider using overlay for the highlight mode instead of screen, unless you wand the walls to look shiny. Making the walls look rougher to match the floor might help make the whole thing more cohesive, though I think the walls look fine as is really. Some grudge on the floors to make it look like the site of battles would be a quick fun way to dirty up the place as well. That advice aside I think its already looking good and going to add a lot to your gaming fun.