This game is awesome. It's quick, it's fun and you're going to replay levels to try to beat your best score. It's in early access, yes, but if the final product is anything like this, it's totally worth the price. I would like to see the graphics improved slightly (there doesn't seem to be any anti aliasing) and support for more widescreen and HD resolutions (like 1366x768) but it is an awesome game.
The price is a steal and the developers are onto something here. They understand gaming doesn't always have to be serious and we are in this to have fun. This game is fun, colourful and you unlock more characters as you go along. Each character comes with a standard and alternative weapon, but they're all different, which makes for interesting combinations in multiplayer. If you're unsure, there is a demo available, though I do believe you're getting more value than what they're asking for it.
As for the technical stuff, it is a top down shooter, which supports keyboard and mouse, or a gamepad. It has local co-op too so that's a plus if you have friends over. As I mentioned before, the graphics could do with a few tweaks, but it is by no means unattractive. The gameplay is fluid and you will be moving around the arena a lot while gunning down hordes of machines. There are powerups available, which also encourage you to keep moving. The music is upbeat and adds to the fast-paced atmosphere.
I'd give it a solid 8/10, with the hope that the final product will be as fun, or even more so.