Penguin Massacre sees you defending your igloo from hordes of onrushing penguins. Like any militant penguin, you're equipped with a pistol, assault rifle, Uzi, sniper rifle, shotgun, grenade launcher and of course a chain gun.
Shoot the oncoming penguins. Switch weapons for the task at hand. Reload tactically. Upgrade your weapons and your defences. You know how these things work, you've played them before, after all.
This one does have penguins though, so it's my favourite.
Penguin Massacre [Kongregate]