I like it

This game is simple, but effective. I like it. I would like to see a couple more things:
1. A system in which you can buy permanent versions of the upgrades, such as coin
magnet or coin multiplier for gems, and/or letting you spend more to get higher upgrades (for example, adding in a +200% coin multiplier)
2. more ways to earn gems. Some games give gems for watching an ad, or they have ways to earn them in game.
3. Quests might be a neat addition as well,
allowing you to earn more coins or even gems.

Pyrodragon82 about Lightning Fighter 2: Space War