It's perhaps not the first thing you'd think of for Half-Life 2, parkour style wall running much like you'd see in Mirror's Edge or Titanfall 2, for example, but it works. It really works.
The Mobility mod has just released it's version 2 release, and as well as being compatible with the base game, it also works with both Episode 1 and 2.
It includes new Melee style attacks, multi-target crowbar attacks, and a surge style attack that lets you fly up into the air or attack from above. It's pretty awesome.
Why Gordon would suddenly be able to do this is anyone's guess - a modification to the G-suit? Of course, that explains it all. It's not too lure or game breaking, actually. It makes the whole thing rather a lot of fun.
I've been playing through Half-Life 2 again recently, and this mod certainly gives it a fresh feel.