I'm playing thru HL2 for about the 5th time (waiting for Oblivion), and man the levels are so EMPTY.
Well, that is the downfall of any game. The emptiness effect was meant to work into the environment of the game. After you play it five or six time, the initial effect of absorbing the game for the effect the developers intended is lost. In other words, like any other game, it gets repetitive after so many times.