I think that the amount of buildable turrets should be limited, `cos sometimes people just put hordes of turrets all around the map and the game becomes uninteresting.((
Well, it would be better if it would be something like a sandbox, i.e. you design your own bombs.
Yeah, it also needs more structures like house, skyscraper, or even a town (for mushroom cloud).
And textures too! It`s a little boring to explode gray cubes in gray universe.