Portal

Unfortunately, I'm not allowed to shortcut my way to any of the other details you might want me to extract. Can they tell me anything new about the Aperture Science Enrichment Centre, in which the game is set? "Not really." They want us to play through. So when I ask when in the Half-Life timeline it was constructed, or if any of the major characters have been there, I get nothing. "All of those questions and the majority you have get answered in the game, or some of those pieces are given to you during the game, and there's also some cross-reference to it in Episode Two." The closest I get to a revelation is when I ask Swift if the levels in Portal are actually physical places within the Enrichment Centre or constructs. Her eyes creep innocently towards an empty spot on the wall and she smiles politely.

One thing we do know is that the main character is a woman who may play a role at some point in the Half-Life arc. Her character model, shown to me during the playtest, is a jump-suited, ponytail-wearing brunette. And slightly telltale is Lombardi's comment when we're talking about the role of story. "I don't think you see anyone other than yourself for 90 per cent of the game," he says, as Swift confirms that there's "no scripted sequence exposition". So hang on, you do see someone at some point? "You'll see when you play, but for a big chunk of the game the only person you see is yourself. A big chunk of it." Speculate away.

Beyond the main Portal campaign, Valve is planning to include additional modes (a Challenge mode where you're either against the clock or trying to do things with as few portals or as little movement as possible, and Advanced, where the hardest levels get harder), and we should definitely expect user-created content, judging by the wealth of content that sprang from the free release of Portal's progenitor, Narbacular Drop. "We have any easy-to-use way of getting maps into Portal and loading them up," says Swift. "We're definitely looking forward to seeing what people create. We're going to be releasing our FGD and an SDK update so people can use what we're using." That should happen soon after Episode Two, Team Fortress 2 and Portal launch together. Don't expect a facility for user content on the Xbox 360 or PlayStation 3 though. "I would love to see that happen but I think the platform holders are always going to need certification, which means it's usually going to have to be a commercial thing," says Lombardi.

Official add-ons - whether new levels or multiplayer - are possible, depending on the community's reaction, but nothing's been decided. "We're still playing it by ear at this point," says Swift, when asked if there have been any developments, "figuring out if we want to do multiplayer next, or Portal 2, or release map packs, and figuring out what our community wants from us as well, but as far as multiplayer goes, we've experimented technology-wise in terms of getting it to work, but haven't really gone into the details of what the gameplay would be like." So it's undecided.

Whether I'm any good or not clearly has been decided, though, as - having spent a good few minutes making it to the end of one particular turret section - my satisfaction at completing a level is quickly replaced with the news that my session is over. I ask Lombardi whether playtesting has any uses beyond simply figuring out whether people get the game. "It's useful to see how somebody reacts to a puzzle because sometimes they try something and it doesn't work, but we're able to use the manner in which they've attempted it as the basis for another puzzle," he says. So you might as well focus your hope on my failure having made a difference. You certainly won't need to focus it on Portal living up to its billing, though - judging by what I'm allowed to play, this could be one of the games by which 2007 is remembered.