Critical Annihilation

Fully destructible world
Annihilate aliens with heavy weaponry
Plenty of explosions and gore.
Leader boards
Achievements
Paintball mode
Killstreaks

wsad to move
<left mouse button> to fire machine gun
<right mouse button> to fire rocket launcher
<ctrl> force to aim at cursor (machinegun otherwise shoots horizontal)
<shift> run
<1> activate special weapon when it's charged, fire with right mouse button.

If the game is running slow, try lowering settings in the video settings menu. You can access it by pressing <escape> in game.