I don't like waiting either, but keep in mind that Valve is a small studio. Since Episode 2 came out around four years ago, Valve have released Left 4 Dead 2, Portal 2, and all that DLC for TF2, and I think we can agree that those were good games.
I am in agreement with the theory that Valve have abandoned episodic development because it still takes a lot of time and resources to make their games, and they prefer their larger projects. I expect Half Life 3 to come out in a year... or two... or when it's done, but in the end, we will probably agree that it will be a much more satisfying conclusion to the series than another five or six hour game.