Pecon, a few suggestions-
1. Maybe possible have a button that when activated, it enables/disables a certain number of events and bricks, such as-
-a-Alternate weapons, alternate bosses
-b-new structures appear, etc.
2. It's getting kinda old with those same classes of bosses and players. Could you add more or change some?
3. Vehicles, like just a simple jeep. no flying stuff.
4. some more music? I mean stuff that get's you really pumped.