I feel like Valve's just been finding new distractions/excuses.
Us, 2007: "Wow, Episode 2 was really good, if a year late... what about Episode 3?"
Valve, 2008: "Look, we just gave you two new games! In fact, here's another! Zombies! Shut up now!"
2009: "MORE zombies!"
"Okay, but now it's been three years since Episode 2, and you haven't had any major releases this year"
Valve, 2010: "Bah, here's Alien Swarm! It's free! And we're really busy making Steam work!"
"Okay..."
Valve, 2011: "You know what, you liked Portal so much... here's a sequel!"
"Bloody hell that is awesome - but what about Half Life 3?"
Valve, 2012: "Counterstrike: Global Offensive! Go away!"
2013: "forget IT OH GOD HERE'S A MOBA KILL ME"
Then in 2014 we found Valve drowning in a pool of tears and haven't seen a game yet - just muttering about how busy they are with Steam. At this point, if they release Episode 3, it will feel like too little; if they release a full game, it will either have to start off really abruptly from Episode 2, or else leave an odd gap. And no matter what, the expectations are just too high.
2016: "...virtual reality?"
Us: "God damnit Valve!"
Valve: "...TF2 matchmaking?"