Who'd have thought that the runt of The Orange Box litter, having been pecked half to death by it's more established and anticipated franchise siblings, would have fallen from the nest not into the waiting jaws of a metaphor, but into a glowing hole in the ground, popping out of a nearby wall, and into our hearts.
Portal is anything but just a pleasing bonus for The Orange Box, and is instead the most intriguing, original, and surprisingly brilliant part of the triptych.
The game is made up of a series of unexplained tests through the clinical confines of the Aperture Science Enrichment Centre, each one a puzzle to be solved using the eponymous portals. Throughout, the sarcastic, disembodied voice of GLaDOS - an experiment-controlling AI routine - guides you methodically from test to test, with promises of eventual cake should you be victorious.
Is this cake a devious and imaginary incentive? Is it chocolate? These are just two of the questions you'll no doubt be asking.
I already know the answers, and as silly as it sounds, Portal is a game just as much about its story and narrative structure as its puzzle aspects. It's far more interesting than Episode Two, and as it all sits in one easily digestible four-hour long lump of gaming, you'll beat it in one gloriously fun sitting.
The portals work thusly. You can have two open at any given time, one blue and one red. These portals are fired from your portal gun using either the left or right-mouse button, and are placed against walls, floors and ceilings. As you enter one, you exit the other.
If you fall through one, you'll fly out the other with the same momentum. If you slap a portal high up on a wall, leap into a deep pit, and place one underneath your feet just before you hit the ground, you'll come screaming out of the wall at high speed, propelling yourself across the room. That, as you might have guessed, is the solution to one of the tests. One of the simpler tests.
The genius of Portal's level design means that every test serves a function, educating you about the initially non-intuitive portals. It's like learning to juggle. The first tests are short, and don't allow you access to the portal gun at all (in essence having you tossing a ball between your hands) and only when you've got a basic understanding of the concepts of portals will it let you go on.
Later, this is helped by the obscurity of some of the puzzles - they'll keep you on the brink of realising the solution for just long enough. You're never frustrated by a test, and equally you're never immediately aware of what you should be doing - a brilliant piece of design work.
Beating the game gives you access to the deeply insightful developer's commentary - easily the best and most enjoyable implementation of Valve's dev-com tech so far - along with a timed Challenge mode, and six Advanced tests (which are re-jigged versions of previous tests, somewhat disappointingly). Having just spent four hours in Portal heaven, this extra content feels somewhat lacking.
You'll work your way through the Advanced levels, but there's an overbearing feeling that there should be a massive series of extra puzzles to play about with. Narbacular Drop, the developer's previous title, was fed a constant stream of extra content by modders, and we can only hope that Portal generates the same.
And it's hilarious. Perhaps the funniest and most well-written (and well-voiced) dialogue you'll come across in a game. You wouldn't think to look at it, with its sobering minimalist design and cold, almost medical atmosphere, but it has more laugh-out-loud moments than anything else I've played. GLaDOS's sassy personality makes every line a delight, and the brief appearance of a silent, yet reassuringly weighty companion halfway through (no, not Gordon Freeman) provides just a touch of emotional drama.