Well, in my opinion, I would get Gothic 2 or Divine Divinity (DD). Beyond Divinity is a continuation of the Divine series so to get the most out of it I would play DD first.
Gothic 2 is a great game. The gameworld feels much more alive than any other game I've ever played. NPCs actually keep schedules, they work certain hours, and go to bed at night (a great time for thievery). The story is pretty good. I can't say enough good things about this game.
However, DD is a stellar title as well. The gameplay is excellent, and the 2D graphics are beautiful.
Its a tough decision, but one only you can make. <img src="/ubbthreads/images/graemlins/delight.gif" alt="" />
"Wizard's First Rule: People are stupid" - Zeddicus Zu'l Zorander