I personally think they're retooling the source engine and working on a more full fledged game, maybe Half-life 3. Whatever it is, I have no doubt it will be quality so I have no problem at all waiting for it. I have plenty of games to play in the mean time.
I learned a long time ago to stop buying into hype, giving much attention to previews, or paying any heed to release dates unless they're confirmed for later this month. I personally think this enhances the enjoyment of a game because you go in without hyped up expectations. Just waiting until the game comes out instead of eagerly anticipating it generally generates more realistic expectations - at least for me.