I am just waiting for Valve to release the part with the dune baggy being chased by that flying alien chopper thingy. That was the most amaizing scene of what I have seen of Half Life 2 so far, IMO.
While that scene is nice, the one thing that needs tweaking is the popup grass. Watch the E3 video and notice how as the jeep is driving around grass pops up not too far ahead. Their LOD system needs to be more subtle than what that video showed.