WARNING! SPOILERS AHEAD!...
Valve's episodic gaming plan has brought one unintended bonus to gaming: gossip. The abrupt endings and foreshadowing of Half-Life 2's episodes are perfect petri dishes for ideas and speculation to flower. And we're nurturing them right here.
Note: the 'facts' here are educated guesses. We have had a word in Valve's ear on more than one occassion, but we'll let you make up you own mind.
A LONG TRIP NORTH
Episode Two ends with the human resistance having won a vital victory against the Combine. Now comes the hammer blow: somewhere, hidden on a long-lost research vessel named the Borealis, just discovered in the Arctic, is a weapon Dr Kleiner says "could shut out the Combine for good."
The Borealis was the star research vessel of the Aperture Science corporation - the same company that invented the Portal gun. Kleiner explains that the Borealis "vanished" from its dock and hasn't been seen since. Maybe it disappeared because we made it disappear.
Maybe the final destruction of Glados in Portal, and the crazy storms that appear, are what teleports the boat to the frozen north. Start packing your thermals: we're going to the North Pole.
Valve initially planned huge battles in HL 2 before they got cut. One is detailed in a short story by writer Marc Laidlaw that sets out a massive battle at 'Weather Control' where the Combine take on the resistance, including Alyx and Gordon... set in a snow-bound desolace.
GLADOS TO SEE YOU
As the end-credits of Portal roll, Glados sings, "believe me, I am still alive." She's sitting pretty in the Borealis, waiting for some new company. We reckon you'll first ally with her against the Combine. She'll make a great friend, but fearsome foe. Once the Combine are dealt with, she's bound to turn on you.
SWAP BARNEY FOR ALYX
Would you drag a grieving daughter half-way across the world into a war-zone? It's a cruel prospect, hence, our belief that Alyx won't be following you to the Arctic circle. Don't fret, we'll still have a friend. Barney hasn't been seen since Episode One... maybe it's time to bring him back?
THINKING WITH PORTALS
Will Episode Three feature a Portal gun? Tim says "Yes. Because that's what everyone wants, because the entire storyline has taken a giant diversion to introduce Aperture Science into the mix, and because it would be unbelievebly cool." Tom says "No. HL 2 depends on realistic settings: settings that would be instantly broken by a Portal gun." There's a 50p office bet riding on this. What do you think, readers?
EPISODE TWO'S OTHER HIDDEN SECRETS
Lamarr? During the final rocket checks, Kleiner announces: "I'm seeing a payload anomaly of approximately eight-and-a-half pounds". Remember the sequence when you're at the tip of the missile? Watch for Lamarr. She ends up in the rocket. Expect much wailing and sadness from Kleiner in Episode Three over his lost headcrab.
Lost When you're ordered down to Silo 2, the room containing the Vortigaunt Uriah contains a hidden room just behind a large tank. You can jump on top of the tank and peer into the room, where there's a Dharma symbol and a computer with numbers on it. Both relate to TV drama Lost, which has included allusions to Half-Life.
Gnome In the first room you enter, where Alyx first makes contact with the resistance, check under the bed nearest the stairs. There's a gnome there. If you manage to carry him through the entire game, you'll get the Rocket Man achievement.