For dungeon type games, you might want to transition to black the ceilings/solid rock/etc, if they're not visible to the player on the ground.

I think your floor is very nice.

The previous artist has run against the overhead-with-some-perspective problem with the vertical door I see - it's larger than the horizontal door. This isn't a simple problem to solve, as you want all floor tiles to remain visible rather than being obscured by walls.