When is a sequel not a sequel? When it's Half Life 2: Episode One, the confusingly titled first new episode in a trilogy of releases that picks directly where HL2 left off. So it's part two of Half-Life 2, but episode one of three of part two? Something like that. Even Valve boss Gabe Newell seems exasperated with trying to justify it. "We should have just called it Half Life 3: Episode One, but it's a bit late now," he chuckles. Actually, Aftermath worked pretty well..