Okay, that was a great opening scene. I don't know about anyone else, but at first Lauri and I were thinking it was a Locke flashback -- the music, the old equipment. Then when the person heard the "Boom" we realized "ohmigod, this is INSIDE the hatch!"
Kate better not be gone.
The scene with Walt freaked us out. We already know Walt has some sort of psychic powers. Maybe that was some sort of image he projected to contact the others for help?
Kate better come back okay.
Years ago (8? 15? definitely longer than 4), Jack worked to save the life of a young woman with spinal damage and was convinced she would never walk again. After Jack meets this stranger named Desmond, she can. Now, the plane crashes on the island and Locke can walk, and guess who we find on the island? Yep, Desmond. Coincidence? Not on this show.
Magic? Some sort of advanced science? Or what?