No control guide but I guess it is like air fighter control, thus don't have a lot of issues with it.
Difficulty only change the speed of spreading plant spikes, but I think as long as I have shot at the planets with the plant spikes, it will be considered as a hit.
Good looking 3D voxel-alike graphics, but could use some audio, maybe at least shooting sound must have, thus it will not be boring at all.
Well, another great 3D air fighter alike game to play!