The game has now entered public alpha stage and the first public version has been released!
After changing my mind countless times I ended up including full multiplayer support in this release. There are currently total of three single player levels and two multiplayer levels, four weapons and one enemy type implemented. The level editor is enabled as well. As this is the first public release and the game has not gone through extensive testing, I'm expecting quite a lot of bugs to be found. Also, keep in mind that the game is nowhere near finished yet.
Downloads have been uploaded for Windows and Linux (both 32 and 64 bit versions). Download it, try it, and report back if you run into problems or just to tell your opinion!