I guess it’s just free. Not sure.
Found this bit of advice from RPS:
“It’s obviously not a complete or comprehensively tuned game, but it’s impressive what a third party can do with a good sprite sheet and a few 8-bit tracks. There’s not much subtlety to it, with simple two-button NES style controls, but there’s a nice rhythm to dodging sniper fire and crouching behind parked cars…While a cute piece of work, it could still do with a little more tuning. On Normal difficulty, enemies do brutal amounts of damage. While generously checkpointed, it does feel like jumping straight into the deep end of the NES-era pool. The gamepad controls are also a bit weird, seemingly not rebinding properly and mapping movement to the left analogue stick. I’d suggest unplugging any controller first and using the more configurable keyboard controls. Not ideal, but still better.”
Worth noting, if you shoot really close, it does extra damage (I’m guessing double). Sort of a melee move… But shooting. You’ll know you did it right when you shoot downwards. It’s also useful for enemies that have the brains to… Crouch.
That and the credits is a survival mode. As in, you literally fight while credits are scrolling. I can only get to the last enemy, but I’ve never beaten it despite beating the main game on hard difficulty.