Halley's Comet sweeps past Earth roughly every 76 years. Throughout history, it has captured the world's imagination with each pass, appearing in the Bayeux Tapestry in 1066 and on TV at least 400 times a day during its last visit in 1986.

But what you may not know is that on its 1835 fly-by, a mysterious substance fell to Earth from the comet. In 1870, a scientist named Dr. Hebble Gate made a spectacular technological breakthrough with this material, which he named the Halley Core. By harnessing its amazing forces he generated a new energy source that changed the world, rapidly advancing mankind's development. Space travel soon became a reality, and the British Empire went on to colonise numerous distant planets.

By 1906, Dr Gate - now the most famous, rich and powerful man in the world - had mysteriously vanished, along with large numbers of deep space colonists. A high-tech protection force, known as Gun Valkyrie, was dispatched to far-off planet Tir na Nog to find out what off Earth was going on...

With Gun Valkyrie taking place in this alternate version of the early 20th century, it has a wonderful style, mixing alien worlds and space travel with steam-powered machinery and clanking cogs, along the lines of Jules Verne's classic sci-i stories. It also means you end up playing with strangely limited futuristic technology, so as well as fighting against hordes of mutant insect freaks you're simultaneously battling with your equipment.

The general idea in most levels is to simply track down and destroy all the enemies. The tracking down bit is easy enough, thanks to a map showing where every beastie is hiding, but actually manoeuvring your Gun Valkyrie character into position and destroying the enemies is where the real challenge lies.

The controls are a bit unusual, you see - when on the ground, a Gun Valkyrie isn't particularly mobile, making scraps against swarms of fastmoving alien spiders very tricky. The weapons are slow to fire, so simply running up to the enemies and letting rip isn't going to work.

Instead, you need to be a bit clever. Your suit - known as a Gearskin - is fitted with a limited jetpack and at first, it seems to be there just to let you jump a bit higher than normal.

But because you can use it to boost as well as jump, the suit is actually the key to getting through all the stages and racking up the best possible scores and ratings in each mission (more on that later).

Clicking the left analogue stick in makes you dash in any direction either in on the ground or in the air, enabling you to manoeuvre into safe shooting positions. You really need to train yourself to think in 3D, as well. Enemies attack from every possible direction, forcing you to constantly figure out the best way to get a clear shot at them while avoiding being caught in the crossfire, or running out of jetpack fuel and falling into some painful abyss.

It's all pretty basic stuff: you shoot things, you collect things, you beat some bosses and you earn points with which to upgrade your weapons between levels. But as you progress through the game, you're forced to learn new skills for each new type of level until you're battling the final boss and doing things you never thought possible early on in the game. It's only when you finish Gun Valkyrie once that you really feel as though you know what it's all about, making the second time through a very different experience.

For example, first time round you'll be awarded a big bunch of 'D' rankings at the end of each level, not earning enough points to buy any of the really good stuff. But second time round you'll be going for perfect 'S' ranks in every area.

The core task is learning to use the jetpack to the full. You'll start off doing everything you can from the ground, but will soon be forced to get the hang of clicking the left thumbstick repeatedly to dash around in the air. If it sounds a bit fiddly, that's because it is. It takes a certain kind of person to persevere through what seems to be a basic, awkward-to-control, very tough shooting game just so they can go back to the start and do it all again with newly mastered, even-more-awkward-to-control skills.

And while it's possible to do some amazing stuff once you've got the hang of things, the frustrating aspects of the game are never far away. The slowness of the controls doesn't mix well with the speed and mobility of most of the enemies you come across, leading to lots of occasions when you get hit unfairly. Add to this the fact that many sections are swarming with enemies and things soon get nasty.

It's also very hard work on your fingers and controller - you're constantly whacking the analogue sticks around, clicking them in and rattling away on the triggers - all the while gripping the pad as tightly as possible. With the frustration levels as high as they are, expect to smack your controller into things regularly, too.

The final boss brought on a stinker of an office-wide headache - partly through the intense, practically-in-tears frustration of the stage, and partly through whoever was playing (mainly Ed) bashing the controller repeatedly into their forehead after each death.

This is the only game that any of us have ever played that's practically reduced players to self-mutilation. We even went hoarse from screaming at the screen swear words we didn't even know existed. This isn't a game for the more casual Xbox gamer, that's for sure.

There aren't many levels (15 altogether), there isn't much variety, there are only a few types of enemy, only two weapons, the level design is fairly bland, the controls are slow and it's extremely frustrating to play.

But at the same time Gun Valkyrie is a spectacularly cool game with a great theme, loads of techniques and skills to master, levels built around an advanced playing style, some extremely challenging stages, a rating system that constantly gives you something to go up against and wonderful graphics and sound.

This isn't what you want to hear in a review of a game, but you need to figure out for yourself whether or not you're going to like Gun Valkyrie. If you like something light-hearted and enjoyable, save yourself from a world of pain and stay away. But if you've got the skills, and fingers, balls and a forehead of steel, get stuck right in.

1. Looks and sounds lovely
2. Original controls
3. Challenging, with lots to learn

1. Excruciatingly frustrating at times
2. Quite short if you're not into Replay

Power
Lovely effects and characters, but scenery is quite basic and there's some slowdown in big boss fights.

Style
Wonderful setting, complex-but-interesting story, cool characters, hardcore approach - very stylish.

Immersion
Intense gamers will want to play through moments that will have normal people switching off.

Lifespan
Tough but short - the replay value comes from mastering everything about every level in the game.

Summary
A no-fills gaming purist's dream, not for the faint-hearted. Intense, skilful action all the way.