Yeah, I don't think Valve's current releases are experiments for the Ultimate Game. They might take what they've learned from previous titles and improve it for future releases sure, but that's what any good game developer does. Besides, if there was such a game that applied the Cooperation of Left 4 Dead, the puzzles and writing of Portal, the action of Half-Life, and the multi-player experience of Counter-Strike,Day of Defeat, and Team Fortress; the world would implode in on itself from sheer awesomeness.