The gameplay of Tommy Gun is quite basic. It is a rail shooter with a third person perspective, where you take out your enemies one after the other scrolling from side to side. Each of the five levels have their unique setting and enemies. For example in the super market level you fight against vegetables and in the Paradise Island level you fight against crabs and pirate parrots, just to mention a few.
If you free the prisoners you'll get extra ammo, health packs, shields and other stuff that will help you stay alive a little longer. There is also a two player mode where the second player takes control of the sidekick Big Cheese.