I own none of them and have played none of them. Which one would you recommend I pick?

Get Witcher 1 as it's only 4.99 at the moment still I think and if you really like the first game you should get the sequel here as it's the best price here and has the best goodies = )

Gothic 2 or Divine Divinity are the two best on the list. Gothic 2 for the more skill intensive but rewarding experience or Divine Divinity for the Diablo-esque experience. Both are good open world games.

I went with Divine Divinity. Thanks for the input.