It's a decent twin-stick shooter, easy to pick up and play for short lengths. Controls are clean, it works well on mouse and keyboard, and it's forgiving enough on some levels to be comfortable for beginners. All you need to know is movement, shooting, and using the short-range bomb as a shield from bullets.
The game has many levels, with the harder path requiring higher scores to unlock. Gameplay is varied with unique challenges available after completing those levels. Scoreboards have been broken for awhile, but what does that matter? It would be topped by a few cheaters unless the devs did regular wipes. And if you are looking to sit on top of a leaderboard, find an unpopulated game.
I play games for gameplay. The gameplay here is solid, but levels can get a bit challenging at times, so I don't play a lot. I usually play for a short period to pass some time, and the game works for that. The lives system seems unnecessary since all levels can be restarted and replayed at will. But the game does twin-stick nicely, and 50% off is a great deal.