It all turned out to be surprisingly simple, really.
The Island is at the nexus of power on the planet. Or perhaps its a big sentient alien blob. Whatever the reason, the area has a frakked up space-time continuum that causes people to become unstuck in time, both mentally and physically, heals people, causes the dead to come back to life and/or causes people to see hallucinations of the dead, enhances polar bear intelligence, alter the laws of probability, teleportation and other fun stuff.
Some of these effects happen outside the Island, or continue after you leave the Island, but the "controls" seem to be located on the Island itself.
The monetary value of all of this is obvious, so powerful people are battling for control of the Island, which is made much tricker since the Island seems to have an opinion about it and can take steps to frustrate or help one side or the other.
There are still a lot of unanswered questions, for instance, has this been going on since the time of ancient Egypt and if so, do the Goa'uld have anything to do with it? But to me, the basic situation has been explained. In S6, I'll just be having fun watching the endgame unfold.