Well, sorta. It's the ragdoll demo for the Havok physics engine that HL2 uses, which is more HL2 than anyone not affiliated with Valve is playing at the moment.
Incidentally, it's fucking neat.
PLAYABLE HALF-LIFE 2 DEMO! HOLY FUCKING SHIT!by SBDMT 07/11/2003, 3:18am PDT CS: Condition Zeroby Live Studio Audience 07/11/2003, 3:31am PDT