In real space, almost everything is monumentally far away from everything else--so much so that collisions rarely happen. In Slingstar, you play a little spaceship in a black void full of things that love running into you. To prevent these collisions, your ship is equipped with "wingmen"--tiny little indestructible ships that do their best to stick to a close orbit around you. Why you bought indestructible wingmen but failed to get even a shred of armor for yourself is a bit of a mystery, but it's probably not worth thinking too hard about.
Slingstar features 60 levels and a truly wide variety of enemy types. Some simply drift past, some act like heat-seeking missiles. Others function like the classic Snake game, leaving a collidable tail in their wake. You'll encounter asteroids (yeah, from Asteroids) that break up into smaller pieces and even the original ships from that game. To survive this onslaught, you have only your wingmen. A single touch from any of the enemies causes your ship to explode. To get your wingmen to collide with anything, you've got to sling them into them by using the somewhat-physics like orbits to behave like you'd expect. Instead of flying or shooting straight at things, you tend to fly past hoping the drag will slide the wingmen into the bad guys--or simply standing in place and spinning furiously.
The mechanic is fairly similar to Gum Drop Celestial Frontier, but doesn't feel nearly so laborious in Slingstar. Because your focus is on your wingmen and the enemies, death can sometimes be surprising--you have to really pay attention to where your wingmen are AND your main ship. While death is common (some levels are pretty hard), the cost of failure is low. There are no lives in Slingstar--after dying you merely restart your current level. Even on the harder enemies, it's possible to just avoid them for awhile and wait for a helpful powerup to spawn.
Because there's no penalty for death (other than restarting), the game takes on a bit of a meditative feel. Though failure is common, the entire thing has a very relaxing feel to it. Besides AI, each enemy has a subtle lighting effect and makes a different sound when it explodes. The unique mix of enemies in each level gives that level its soundscape and visual display--reminescent of something like Rez, but not quite so experimental.
Besides the rank-and-file enemies, there's also some pretty spectacular bosses that I won't spoil. I made it through about half of the levels in an hour or so, so there's not a ton of gameplay. At only $1, though, Slingstar is definitely worth the points.