In the past, the first game that actually featured Source was Counter Strike Source. Half Life 2 came out after CS: Source. Base on the recent DOTA 2 fan's photography of the Valve's computer log, we knew Source 2 and L4D3 are in progress which could mean, the first Source 2 game will be L4D3. I am fairly certain Valve is working on HL3 and I am betting the game will be much larger, perhaps more like an RPG since HL2 format is no longer sufficient and generally, HL2 is very rich that can support RPG.
Half life 1 was about the graphics for me back then , the game itself was like doom , Unless they make it like farcry 3 and really change the way the game acts then I dont think anyone really wants it. Make Portal 3 Instead , Thats a real game.
HL3 isn't going to happen any more than any of us have a shot at dating the next SI Swimsuit Edition cover model. Let's just acknowledge it and move on for God's sake. As much as I want it. Stop wasting time and internet bandwidth on speculation BS.