H.E.D.Z.: Head Extreme Destruction Zone is an action/shoot-em-up. You play an alien capable of wearing different heads, and the goal of the game is simply to engage other aliens in combat, kill them and collect their heads, ultimately trying to collect as many heads as possible. You can swap heads in and out of a backpack (which only holds 5 heads), and at the expense of points off your score, out of a store of all the heads you've collected (out of a possible 225).
Each head gives you different powers (weapons, shields, weapons, speed boosts, weapons, etc.). There is an element of strategy (in that you have to pick a good set of heads to avoid spending points on unnecessary swaps), and some heads only have a limited operation before you have to swap to another head and let it recharge.