The worst thing to happen to HL2 was the code leak. It effectively led to a whole host of things being redesigned on the fly in some sort of attempt to invalidate the build that had escaped into the wild. Truth is that people would've bough HL2 in it's original form whether there was a leaked version or not.
Valve hit the panic button, and as a result we got a game far less beautiful or entertaining that we should have.
The lesson here children, is stick to the project development plan and content designs you spent years making, as opposed to the ones you drew up in five minutes.