The four game modes are:
Megagore: destroy everything and avoid all the bombs and enemies.
Dodge This: you have to collect as many boxes as possible and dodge all enemies as you don't have a weapon.
Assault: this is it, fight to the death, trust me, you will die!!!!!
Chromatic Conflict: shoot enemies the same colour as your ship, enemies spawn different colours and you have to change your ship colour at one of your bases to suit.
The game is pick up and play genius, trust me, you will be addicted.