Boxhead: 3D (also marketed as 'Boxhead: The Zombie Wars 3D') features updated 3D graphics compared to previous Boxhead games and there is a new coin system, coins being available from defeated in-game enemies or via purchase for money. Gameplay remains the same, defeat as many waves of zombies as possible before you are overwhelmed.
From the developer:
Play as the black-clad mercenary Jon Bambo and stay alive against wave after wave of flesh-eating zombies with an arsenal of deadly weapons. Collect the coins, items and firepower left by your fallen foes to upgrade your guns, replenish your health and unlock new stages and characters.
Start with a hunting blade and cycle up through bigger, beefier weapons as you annihilate more foes. It's kill-or-be-killed, so fire wisely and try not to die!
Source: The Developer Website.