Portal was special.
It did away from the almost universal gaming line of conflict as competition, which usually ends up with someone getting shot in the neck or punched in the ear.
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It represented gaming beyond primal thrill-seeking, and reassured us that there was still space for patience and intellect in our hobby.
It felt important.
Only problem was, it was tiny: A four-hour title nestled away on The Orange Box. It was never meant for a full release and perhaps better described as an 'experiment' or some whimsical "What if...?" project, rather than a full game.
With the coming of Portal 2, though, Valve's original flight of fancy can now be considered more of a prologue to what promises to be one of 2011's most interesting, challenging blockbusters.
For Valve, amping up for a full fat release isn't just about making Portal more taxing, however.
"The easiest thing that we could have done was to just make it more difficult," says Valve's Chet Falisek "But instead what we've done is expanded the complexity of the tools we give you.
"It's a much bigger world, you meet a lot more characters, explore more spaces, the puzzles are expanded and you have a lot more tools to solve them."
What kind of new tools? Well, the most obvious is the addition of a partner in Portal 2's new co-op mode.
Taking away the human touch of single-player's Chell, a pair of puzzle solving pals take control of two self-aware Aperture Science robots, which GlaDOS is pushing through the Co-operative Training Initiative.
They're an adorable duo - in that kind of emotionless, Valve way - with basic communication through little more than a few bleeps and a flailing gesture should you require it.
Should you be concerned that the introduction of this most 'traditional' of elements will somehow cripple Portal's hermetic intellectual appeal? That it will somehow become dumbed down to shoehorn in a feature for the masses? Of course not. This is Valve, you ninny.
In gameplay terms, your duo of co-op bots gives you four portals to work with rather than two - but you're going to need all of them. Although the puzzles are naturally more complicated in design - you've got two bodies to get from point A to B, rather than two - the helping hand helps even the score.
What ensues is probably one of the best virtual team-building exercises ever created. It doesn't take long during our half-hour hands-on with Portal 2 to realise that the game's co-op mode can't be completed without communication - and lots of it.
Although things start out incredibly simple, you'll soon find yourself standing within four clinically white walls, pondering how to work with your partner who's stuck on the other side of a portal-rejecting pane of glass.
In the section we play through, we use portals to fling ourselves to unreachable buttons and open gates to give 'player two' access to weighted cubes - which can then eventually be craftily dropped it into a dock to release them. Sounds simple. Is anything but.
Our experience with Portal 2's co-op has a clear momentum. Although we're given some of the easier puzzles to ponder (we're assured this has nothing to do with Valve's opinion of CVG), the starting point is always the same: a look around and a good, hard think. Then, once one of our enforce pairing manages to crack the first step, the second usually revealed itself.