Just had a quick tryout of Onslaught! Arena - it's one of those shooters where you control movement with the WASD keys and shooting direction with arrow keys or mouse (mouse control is better as it allows much more precision).  Both the graphics and sound have a real retro feel to them, and if you liked some of the classic single-screen 8-bit or 16-bit shoot-'em-ups, you'll definitely enjoy this.  There are plenty of different enemy types, each with different behaviour patterns, several weapons and a boss to beat every ten levels if you want to be able to save your progress.