I've done some more pretty cool stuff on the game in the last weekend. I've implemented 4 player multiplayer, multiple levels, moving enemies and crazy bulletpatterns. I'd say thats quite a lot for a weekend! The game is pretty retro, and each level starts by enemies moving into place and then start to spray bullets all over the place. Some enemies work as a shield for the shooting enemies and since you can only shoot straight up, you have to penetrate the blockade to get to the shooting enemies, without getting shot of course! Once all enemies are dead you move on to the next level. Oh and I almost forgot, there are loads of powerups! I'm having some trouble though. If you shoot all enemies that shoot back first, you end up with a lot of enemies left that just stand there and do nothing. It feels pretty pointless to kill them all when they aren't returning fire. And I can't have ALL enemies fire, that would make the game insanely hard. I'll figure something out, suggestions anyone? :D  
Here's another picture of some new enemies firing bullets at me!: