Half-Life 2 makes me sick. Not in the way that it is doubtless making rival developers sick, in that it’s so astonishingly good, has so casually raised the bar way beyond what other games are doing or even had thought of doing. No, sadly, this masterpiece gives me stomach-churning motion sickness. Some people get it with any FPS; the Japanese are known to be more susceptible. But it’s not something I’ve experienced since I watched a friend complete a level on Goldeneye purely by slapping the enemy around. Back then it was a combination of alchohol, low framerate and watching, rather than doing, that made me feel queasy. Here I don’t know what it is - I’ve tried widening the field of vision and reducing graphics settings to near-3D Monster Maze quality, to no avail - but I can’t be Gordon Freeman any longer for the moment. The depressed citizens of City 17 will have to suffer a little longer without me. Sorry, guys.

So I can only offer a partial, provisional list of little things I love about Half-Life 2. The way Freeman never speaks, and the way other characters turn this into a running joke, is a perfect riposte to either the clunky choose-your-own-adventure-style dialogic choices offered by such games as Deus Ex, or the way other games just don’t notice that you float through them as dumb as a plastic mannequin. The abundant wide-open dynamic spaces give you a sense of tactical freedom, but are also designed with exquisite subtlety always to channel you in the right direction. You’re thrilled at being hunted, yet you don’t feel as though you are being herded through a linear maze; somehow you just sense that one way is the right way to go. And you’re always right, which is to say that the game is always right too.

The city itself is a masterclass in downbeat beauty. When too many games resemble the result of a riot in an art director’s studio, all clashing styles and lurid colour-schemes, the subdued hues and dramatic skies of Half-Life 2, along with the attention lavished on the despairing expressions of the downtrodden populace, add up to something approaching a tragic aesthetic grandeur. We could talk physics, weapons and vehicles, too, the whole box of toys that the game offers, but for me a large part of the genius of Half-Life 2 is a crane glinting near the horizon in the distance, or the pink hue of a sunset sky reflected in rippling water. This is an environment that has been given character through countless tiny touches, through the fears and dreams of its inhabitants. It offers an unparallelled sense of place, filled with foreboding and threat and yet a hope that beauty might survive the conflagration.

But, as I said, I can’t go there any more. So instead I go outside to get some fresh air and explore the new city on my doorstep, which is Paris. I’ve been visiting this area in the 18th arrondissement regularly for over a year, so it’s not entirely novel to me, but there’s a lot more to discover when you actually live here. Just as with a Grand Theft Auto game, you start off bewildered by the scale of the place, and quickly learn a few major routes to places of interest. Then you start exploring nooks and alleyways, and learn some shortcuts. Before long you automatically know how to get to a few familiar pay-’n'-spray facilities and gunshops - or, as it may be in my somewhat less crime-infested neighbourhood, cafés and patisseries. It’s funny how the process of learning a virtual city has become so close to the process of learning a real one, and how strategies for the former can inform the latter.

Game culture is pervasive here, too - my local métro station is plastered with huge poster ads for San Andreas. But there is also the delightful, whimsical and oddly haunting phenomenon of the mosaic space invaders. For a few years, an incognito artist has been placing little space invaders made out of small ceramic coloured tiles on the external walls of buildings in Paris. They wink at you as you turn a corner, or gaze down at you through your café window. Other people, from time to time, come and remove the mosaics. When this happens, the artist returns and writes a score in the space vacated by the alien - it might be 5 points or 10 points, depending on how difficult it had been to capture (height above ground, accessibility of nearest window, and so on). The creator and his devoted pilferers are locked in a slow-motion game, which turns the environment into another kind of virtual playground.

Thus I have been exploring City 17 and the City of Light, the one calling to me from the other, the second an escape from the first. I hope to be able to return to Half-Life 2, nurturing the hope that some recondite technical setting might ameliorate my nausea, but for now the rooftops of the real city symbolize a new challenge.

And that, readers, is my Paris game life this month.