Three versions. Original: Free, Upgraded Inexpensive. Modern: Worth it. All the same game and story, just built in different eras.
Pros: A great story, great characters, great dialog, and missions that you don't mind doing. I thought I read somewhere it was like a 3d version of Twinsen's Odyssey. High praise.
Cons: Key layout a little odd. Player angle sometime awkward.
Tip: Do not kill the hunter. He is your friend.