"none of the organic textures and curved surfaces seen in Prey, Quake3 or even the Unreal engine. Now I know this is more of a tech demo but it's still a bit under-whelming."
Personally, I'm getting sort of tired of the "look, you're playing inside a giant alian vagina!" gimick and I don't find it particularly exciting either technology wise or style-wise. The HL2 has its own style that's quite slick and nice. So what?
"A machinegun is a generic weapon, much like knives, plasma guns and rocket launchers. Portals, however, a lot less generic. "
And yet, they've been around since Unreal 1. Did Prey rip it off from them? It's not technology, its how you use it, and Valve has been very adept at none only creating flashy features, but actually employing them into well-thought out gameplay.