Huge, expansive levels even on the ZX Spectrum, and lots and lots of action and colourful graphics which actually get better as the game goes on.
The gameplay was essentially a matter of running from left to right whilst firing constantly in all directions - which is true of many games, but moreso in this case. The screen only provides a small 'window' into the game world, and you often find yourself leaping towards the right edge of the screen with no clear idea of where you will land. The 16-bit and Commodore C64 versions apparently had a very good soundtrack, which was not present in the Spectrum version.
The Bottom Line
This was part of a New Wave of Platform Games, combining the fast action of console titles with the weapons and upgrades of shoot-em-ups such as Nemesis/Gradius and R-Type. It was notable for its enormous levels and its impressive sense of scale, and the game is fondly remembered nowadays. It would really benefit from having a much larger screen resolution, and the enemies are often unavoidable, but it's good fun; a bit like the later Commander Keen games, but with weapons. The graphics and general architecture had a metallic, and later bio-mechanical look to them that was very influential (and widely copied), and the idea of having a gun that you can rotate around you like a wand was very clever although it might have been first used in "Midnight Resistance". Indeed, Turrican managed to provide a contemporary arcade game experience on a home computer, and was a particularly impressive feat on the aging Sinclair Spectrum (it was a boring multiload, although I think the 128kb version reduced this to a degree).