So, what game could possibly be interesting enough to pull a fellow away from Grand Theft Auto IV for a few hours?

Portal, of course.

Or, more accurately, a user-made Portal prequel.

I spent a big chunk of my yesterday working through over 40 new and bedevilling test chambers that are part of a map pack available for download here. These new trials tell the story of test subject 15837, who, we are told, was long ago tasked to navigate a completely different Aperture Science portal maze than that of the subject whose wiry, hydraulic-powered shoes we stepped into in the original Portal.

It perfectly captures the atmosphere of Valve's game, from the laboratory's background hum to its grey concrete walls. It even borrows and repurposes lines uttered by that infuriatingly chipper and untrustworthy computer voice that accompanied players during their first experience as an AP test subject.

Of course, there are parts of this user-made add-on that lack the polished design that only comes with the resources of a top tier game studio (the test chambers, while undeniably challenging, often lack the intuitiveness and efficiency of those found in the original game), but considering that this is a free expansion the same length as a game we paid for, it's hard to complain.

The biggest bummer is that this map pack is only available to those who purchased the game for PC. Xbox 360 and PlayStation 3 Portal fans are out of luck.

Still, console fans can play the original, user-created Portal offshoot upon which this collection of test chambers is based. It's a beautifully animated 2-D homage called Portal: The Flash Version. It's free and requires no local installation; perfect for workers who need a quick Portal fix during the day. You can play it here. It's worth playing before downloading the new map pack if for no other reason than to see how the developers translated levels from their 2-D game into a 3-D world.

Speaking of the folks who created these games, both were made by a collective of coders called wecreatestuff, who self-describe themselves as “a group of nerds with way too much time our hands.”

Pretty much my favourite kind of people.