[Update]: The AMA is now over. You can find my summary by heading over here.
Even though Valve as a whole seems to shy away from any sort of community interaction Gabe Newell is surprisingly approachable, so much so that he has a public email address where he takes the time to answer fan questions. But even still I must say I am impressed that someone as busy as Gabe Newell has decided to, at the behest of a single fan, host a Reddit AMA so that the entire world can grill him endlessly about Half Life 3!
On January 17th at 11pm UTC / 3pm PST / 6pm ET Gabe Newell will appear on The Gaben subreddit and host an AMA (Ask Me Anything). The choice of subreddit is a bit... questionable given that The Gaben appears to be mostly satirical in nature, but if nothing else the comments are going to be rather interesting!
While I obviously don't know how the AMA will go, I have a feeling Half-Life is going to be a major point of the conversation, closely followed by Dota 2's most recent and occasionally controversial Update 7.0. Beyond that I would like to see some answers about the future of Steam Machines, the Steam Controller, and Valve's role in the growing VR industry. And naturally, whether they plan to actually create any new games given that it has been quite a while since Portal 2 came around!
Whatever the case may be, I suppose we'll find out later today. If you don't have the time to participate in the AMA yourself, feel free to stop by afterwards as I'm planning on doing a brief summary.