Presented by Artesneit, Yakouga 2 is another excellent freeware shooter that might be a tad too difficult for beginners. The level indicated on the top right of the screen reflects your weapon's current firepower, while the HP gauge shows how much damage you're able to take before going down in a pool of blood.
Green emeralds increase the amount of time you have before entering critical condition, with the unfortunate side effect of gradual HP loss. The download links can be a little difficult to access but it's well worth the trouble.