Invader360 is a great little Flash based tube shooter, similar to arcade classics Tempest, Gyruss or, more recently, ABA Games' downloadable Torus Trooper. Developer f1ash brings this exotic branch of the shmup tree to life with frantic action and a minimal, well defined style.
Manuever the ship with the mouse, and fire by left clicking. It can take a minute to get used to the way your bullets travel towards the center of the screen, but f1ash is generous; in addition to a gentle difficulty curve, the two lines dividing the screen into quadrants act as crosshairs which mark the point that every shot must pass through. Precision targetting pays off, as consecutive hits will quickly rack up your combo meter and earn big points. You're only allowed to have 4 bullets on the screen at once, another incentive to make every shot count.
Invader360 earns a bit of replayability with random placement of its waves of enemies. Although an overall lack of frills such as music, powerups and colors might turn some players off, Invader 360 is ideal for perfectionists and high score chasers. The game may run slowly in fullscreen for some users, which makes it far too easy. Use this link to play a smaller version.