They said in the interview that they were limited when making HL2. They have noticed many mod teams are enjoying themselves and Valve want to do the same.
Tubgirl lol, I came across that searching for HL2 pictures and then I come here and hear that some idiot posted it all over the homepage and it made me laugh...
I was gonna have a parachute out of the plane map once where both teams start in planes facing each other and they can stay in it shooting each other or jump and freefall, once they hit the floor the teleport zaps them to perhaps another sky so they never stop falling or maybe back up in the plane.
One day when I can make a plane good enough for Source, I might make this.
The headshot thing isn't that hard to make. Rlm had it, it was called megahit and a hit to the head made the player explode with gibs flying everywhere.