Fun little run and gun, awesome 16 bit graphics and side scrolling gameplay. There's always balance issues with games like these especially regarding the weapons; where quite often they're truly devastating to some enemies and infuriatingly ineffective against others. Also the reload times and clip sizes don't match the fast pace and limitless fire power of the enemies.
The upgrades too suffer from this kind of thing, e.g double jump is only useful when certain floating power-ups are just out of reach otherwise you're still just a moving target that's slightly higher as it does almost nothing to help you dodge incoming fire.
All in all a cool game that will undoubtedly get better with updates.