The game is very fast and the smooth animation, impeccable! I recommend the joystick instead of the keyboard if you can, as the game is harder using the keyboard.
The sideways missiles are a nice touch that helps you to defeat the many enemies coming after you.
The downside, in my opinion, is the annoying sound effects which sounds a lot like a TV static and it gets old pretty quick. It is a small problem in a great game.
The version I played is a cracked one, allowing you to play with no life limits. Of course, you should play without these baby features ;)