Coool
I could go on for days about the great level of customization, but I'll get straight to the negative, because authors love that so very much.
The game portion of this Flash is terrible. You got the running and most of the shooting down, but it's definitely missing a few things. The game is slow. I'd run this game non-fulscreen, but then it would be dificult to see all the text in the editor and below the game. I noticed once the player fires a bullet, the bullets follow the player when he moves. It's the same with the enemies when they are shooting up and you jump pass them, the bullet they shot will suddenly go diagonal because they face diagonal too.
Once again, the customization and interativity is incredible. The ability to save files, open the premade stuff, weapon/pickup property inspectors, all great. But it's like putting up new wallpaper on a ghetto shack. It's different, but what's the point? The game isn't really fun, so customizing it doesn't really make it any more fun. Try working on the execution more, since you did well with the planning stage.