I dont really like ARGs, but I kind of respect the work and creativity that goes into them.
That said, this latest phase of the Portal 2 ARG is kind of burning through their stock of goodwill. It violates a lot of 101 Good Game Design principles (Hiding the rules, not providing any feedback) and also manages not to provide any real reward- Despite the thousands of man hours poured into the ARG, we're looking at a release smack in the middle of a workday, about 12 hours ahead of time.
I understand why they can't release the game early, but then why even hint at it? It feels cruel and manipulative and very un-Valve.