I've been working on a better wave/stage system but it needs some more time for basic tweaking and balancing: by next saturday it should be in a playable state for you to check out.
What's happening (work in progress, not in the current build)
- New progression system based on waves (and not stages): it will allow for more randomness and finer tuning
- New 'Traitor/Defector' enemy (let me know which name you like better): a more aggressive viper that can strafe
- Tweaked 'Wing Leader' enemy: will be a bit more consistent in it's behaviour and there will be less of them
- New 'Scavenger' Upgrade: for maximum scraps attraction
- Better 'Armored' Upgrade: boosts hull to 150% but no more extra life (there are towers for that)