It's a decent enough game with pretty retro style graphics. Controls are simplistic in that it's just shoot and jump. The game is definitely difficult. The game is also pretty short. Also, you can't run and shoot at the same time.
My only real complaint is having to constantly spam the attack button instead of an autofire option. Apparently, there are stores that offer weapon upgrades that help alleviate it.
For its price, I'd say it's a thumbs up.