Technically, you still control the man-ish lead character, Zato. He's blind, but has the unique power to see from the point of view of the enemy. If that's bending your brain a bit to understand, here's a picture of the screen when a few enemies are coming in on you.
Thankfully, you're not allowed to move around at the beginning, you just sit with a little pipe up your bum and swivel around. You have two attacks, missile and beam, both of which do varying amounts of damage and both which re-supply over time. It sounds simple enough and certainly doesn't look like all that much, but once you dig into it you'll find it gets increasingly difficult over time.
The reasoning is pretty simple -- there is an absurd amount of enemy types. Some move around the screen, some fall from the clouds, others walk straight at you. Remember, you're only seeing the world from their perspective, so you'll be essentially shooting yourself in the face -- a sensation we can only describe as gratifying.
The enemies come in waves. Once you defeat a wave, you move onto the next level. Then shit starts to get complicated. By level two you can move around freely, while enemies have shields, they move quicker and they're more of a pain in the ass.
Second Person Shooter is an experimental game through and through, but it's still worth at least a glance. It offers a unique gameplay experience that is unrivaled anywhere else and will provide you with entertainment of a new sort. It's hard to see any practical use for the idea, but it's fun nonetheless.
Play it here.