Zombie Hole

You move with the WASD keys and aim with your mouse, which lets you shoot in any direction. The spacebar cycles through a few different weapons you find. Your main goal is to push through the zombies, find a professor for assistance, and eventually close the cave entrance. The pace is constant, with zombies coming from various angles, and it can get quite difficult as their numbers increase. It feels like a tense, focused scramble to survive each wave.