If you go to the fair, and you get on the Tilt-A-Whirl, and acceleration grips the little cart in just the wrong way, and it spins around and around and around, and never slows down or goes the other direction, and if moments after wobbling down the little iron staircase you vent a dozen slightly used Tiny Tom donuts all over your shirt, does that make the Tilt-A-Whirl a bad ride?

Does it make you a dumb-dumb for failing to respect your own limits? Or is it just the randomness and uncertainty we should all expect from nature and physics, and sorry it turned out badly for you this time but it's nobody's fault, and you could probably get back on that thing right now and it would be fine and fun like it's always been before, and it wouldn't get stuck in a four-minute spinloop, and right now that smells awful and you're turning people off their corndogs, so how about you run along and get yourself a wipe? This is not an abstract question. It is important and highly relevant to this week's video game, Darkwatch.

Here is the issue. Darkwatch is nauseating. It is profoundly, deeply nauseating. It causes motion sickness. It makes you feel your pulse throbbing on the left side of your abdomen, just under your ribcage, in the place you only ever felt your pulse once before and that was when you had Norwalk. It fills your mouth with something that is probably saliva but tastes more like sweat. It makes you worry whether it's safe to swallow.

Darkwatch is a first-person shooting game, which means that as you play, you see what the protagonist sees. As he takes each step, the view bobs up and down. As he turns his head, the camera goes with him. As he jumps impossibly high in the air, straining to spot the sniper on a distant cliff, the view shakes and twitches with every dart of his eyes. And because this is 2005 and we have fast computers now, all of it is rendered in smooth 3D. None of it actually looks realistic, but your ape-brain is easily fooled. It sees the corridors and the cliffs moving past, and it tells you that you are in motion. Meanwhile, your inner ear steadfastly maintains that you are slouched immobile in your basement, fiddling with a video game controller. Blindingly intense nausea follows.

First-person shooting games are notorious for making people feel sick, but only certain people and only some of the time. Most players are unfazed, and they wonder what's wrong with those crybabies clutching their sides. There is nothing serious to distinguish Darkwatch from its shooting-game peers. It is a vampire western and you are a vampire gunslinger. Reanimated corpses wearing cowboy hats and carrying scythes swarm all around. You must shoot them in the head or slash them with the giant sawblade attached to your gun barrel. It's standard stuff, really, but it is loads and loads of fun. The creepy enemies make gross wet sounds when they fall down, and the guns are loud and the pacing quick. As a play experience, it is great. Really it is.

What is different, or what at least feels different about this game, at this time, is the queasiness. Somehow Darkwatch has unique powers: it can take a tough stomach, one that has lost count of its Tiltings-A-Whirl but never once lost its appetite, and set it aboil in the time it takes to go from one save-point to the next. If it were not an inanimate object you would swear it hated you.

Maybe it's that the controls are a little jerkier than the typical first-person shooter's. Maybe it's that aiming the little reticle at an undead cowboy's face requires just a few more over-and-back adjustments. Maybe it's that the colours are extra dark, even by the charcoaly standards of the genre. Maybe it's none of these and you'll play happily for hours and then go eat a Muffuletta. Still, try before you buy. If you wanted syrup of Ipecac you could get it for a lot less money.