If you go for Gothic 1 or 2, don't forget to check out mods.
There are quite a lot available, some with a total new story, some with additions.
Sadly there is mostly only a German version of it, but you might be lucky.
Anyway some recommendations:
Gothic 1:
Welt der Verurteilten (http://forum.worldofplayers.de/forum/threads/1274172-Release-Gothic-Welt-der-Verurteilten-v1-03-7)
Gothic 2:
VarusBiker Edition (http://forum.worldofplayers.de/forum/threads/1269453-Release-VarusBikerEdition-v1-4b-3)
Minimod Balance (http://forum.worldofplayers.de/forum/threads/824014-Release-MiniMod-Balance-v2-52-3)
And my favourite mod for Gothic 2:
The Returning (http://forum.worldofplayers.de/forum/threads/1255170-Gothic-II-Die-R%C3%BCckkehr-Hilfe-Info-und-Diskussionsthread-32)
It adds a new chapter, brings back our beloved "Sektenspinner" (sect) guild and is more difficult.
Sadly it's a Russian mod, and there is no proper English translation.
If you check out the link above, there is a link for a PseudoEnglishPatch, which includes a horrible english translation.
For us lucky people, who understand the German Language, a mod-team translated and fixed all bugs.
Check it out, if you haven't already.
Click me! (http://forum.worldofplayers.de/forum/threads/1286243-Release-GothicII-Die-R%C3%BCckkehr-V1-0-2)
P.S: Sorry to kinda go off-topic, but there is no proper Gothic thread :P