Robokill

This impressive Flash arcade game offers furiously fast action, good visuals, great sound, and a surprising amount of depth for a 2D shooter. In Robokill, you are a mercenary robot which earns experience and collects money as you blast your way through a series of rooms with increasingly powerful defenses. As you progress you can purchase new weaponry and items which are equipped in 8 slots on your robot. Standing still is suicide, so the key is to get good at moving and aiming at the same time.