Speaking of terrains, would it be possible to add more variation to the height of the terrain? In Defense Grid 2 there are drastic changes in the elevation of the levels such as some tower placement areas being on top of a tall mesa while others are in a low lying valley that doesn't offer towers much coverage of the map but can serve as a choke point for one of the paths.
This would especially make things more interesting terrain-wise because while the taller tower placement areas would offer towers, potentially only towers with physical munitions like mortars, an increased range, the taller terrain features would also be an obstacle for lower tower placement areas.