Mostly looking at a lot of little touches like having the screen dim and center text when object interacting with 'prop' items (closed door textures as example,) triggers that when walked over will trigger other events in the map for ambient effects, and the like that might be a little tedious but are fairly easy and add atmosphere.
So far the hardest part (assets to one side and disappointment at how few things were included in the charbuilder by default) is figuring out how to stat balance so combat will be fun, not too hard, not too easy, and encounters don't go all sideways.
Must be why dev rooms with 'one of everything' are constantly found in games.