Ah, science-fiction and worm-like leaders are never far apart (Dune, nuff’ said). I never really understood why the Combine would station multiple Advisors on Earth. If they were really that important, why would you need like 20 of them? It seems that if your inter-dimensional trip was a one-way affair, you would leave your most important assets behind to facilitate the logistical aspects of the invasion. I always liked to think the Advisors were hive-minded, slaved together to amplify their latent telepathic and telekinetic abilities.
It was awfully shortsighted of the Combine to invent a teleportation device that can only go to other dimensions and not to different points in the same dimension. If a bunch of monkeys with MIT grads could figure it out in a few decades, how the hell could an advanced inter-dimensional empire like the Combine not invent it first? Plot holes, plot holes…