ABA Games' Torus Trooper is a fast-paced arcade shooter with a beautiful simplicity. Like so many great arcade games it dispenses with plot, background and explanation, dropping the player straight into a colourful and initially disorienting world of shiny polygons, his only objective - to surpass his previous high score.

Playing Torus Trooper, you are given control of a ship which races at high speed along the inner surface of a tube (not strictly a torus, since that would be dull - the track includes many twists and turns, corkscrews and chicanes where the available surface of the track is reduced). A number of enemies also reside in the tube, most of them travelling more slowly than your ship (but in the same direction) and with the ability to release projectiles of several kinds at you in an effort to disrupt your progress. In order to stave off these assaults, your ship is equipped with two weapon systems. The first is a straightforward one, firing large numbers of polygonal 'bullets' forwards at your enemies. The secondary weapon, however, is much more interesting: Holding down the secondary fire key charges the system (accompanied by a sound effect and a slowing of the game, allowing you to evade attacks and line up a shot more easily) and releasing the key fires the weapon, its effect increasing when the button has been depressed for longer. This projectile can destroy enemies and will also clear from the screen any enemy attacks it encounters, giving it both offensive and defensive effects.

Torus Trooper also does away with the genre staple of "lives" - the game is over when the timer in the top left of the GUI counts down to zero, and allowing your ship to be destroyed by enemy fire incurs a time penalty. The remaining time can be increased by reaching certain score thresholds and by destroying the 'boss' enemies, tougher and more powerful opponents which appear periodically. The game is organised into a series of levels, and you can choose to start at any level which you have previously reached.

TT's gameplay is relatively simplistic, the main challenge in the game arising from the overwhelming numbers of enemies faced as you progress and from the blistering pace the game sets, even on its 'Normal' difficulty setting - the 'Hard' and 'Extreme' settings make everything even faster, leaving little or no time for thought; Torus Trooper is a fine example of "twitch" gaming, requiring good hand-eye coordination and fast reactions for success. It is also difficult to do justice to the game's pace in still screenshots (or even to take them without getting yourself destroyed!)

I do have a couple of minor complaints about Torus Trooper - firstly, the (admirably responsive) controls cannot be rebound, although a number of alternatives are given for each command. Secondly, and more importantly, the high score system is rather limited; the game displays only the highest score for each of the three difficulties, and does not allow the entry of a name or initials, so if more than one person plays the game on the same computer only the highest score will be shown. These concerns aside, Torus Trooper is a high-quality piece of freeware, featuring great music, spectacular graphics and fast-paced action almost rivalling PomPom software's recent Space Tripper, a commercial release which perfectly captures the essence of arcade gaming.