This game is Amazing!
It's so much like the great exploration 2D games of the 8-Bit era, like Metroid and Wonder Boy III with some of the flare of todays graphics. Played correctly this game could last you a very long time. I've played most of the demo, and have some 7+ hours in it, and I don't think I've found everything I can.
I can't wait for the Mac version. It plays ~ok in Parallels, but there are obvious slowdowns.