Suggestions:
Right at the beginning there's a little guy walking along, I assume you're going to have a 'protect the citizens' level?
Also (sorry purists) a bit of inertia on you ship, would just make it feel a bit more modern.
Meteor storm level
Hard ass invaders that take multiple shots
Upgrades - Double shot, laser, rapid fire (more than one shot at a time), rebuild defences, fast ship, shield
Right at the beginning there's a little guy walking along, I assume you're going to have a 'protect the citizens' level?
Also (sorry purists) a bit of inertia on you ship, would just make it feel a bit more modern.
Meteor storm level
Hard ass invaders that take multiple shots
Upgrades - Double shot, laser, rapid fire (more than one shot at a time), rebuild defences, fast ship, shield