Outcast

Three versions. Original: Free, Upgraded Inexpensive. Modern: Worth it. All the same game and story, just built in different eras.

https://www.gog.com/game/outcast
http://www.fresh3d.com/outcast11
https://www.gog.com/game/outcast_second_contact

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.