He is the co-founder of Valve and he disappointed fans when he said that Half Life 3 isnt even being developed right now. The developer said that he wants to focus on some other games.
On the good side Newell didn’t totally write off the game ever arriving. He said “…the key is to just continue to follow where the customers are leading.” So if we can believe him then Valve could produce Half Life 3.
The question on the lips of fans of course is when this will happen.