basically, to make the killcount go higher, you need to kill something, then you have (for exampl) five seconds to kill something else. If you do it in that time, the killcount goes up one, if you don't the kill count goes down one. The higher the killcount, the higher score you get by killing one thing.
Awesome game. I only got to 45th on todays highscores.
What douches. You don't just get a pistol. You get uzi, shotgun, cluster grenades, exploding barrels, claymores, ect.
ingame, press 'p', and it pauses the game and brings up a list. this list represents unlockable weapons/upgrades. theres a number at the side of each weapon/upgrade, and that number corresponds with the amount of kills at a time you need. ingame, theres a killcounter, and you have to kill enemies in a certain amount of time to each other to make it higher, thus unlocking things.