IMHO Gothic 3 is an awful lot better than Arcania; I can't speak for the earlier games in the series, I've been put off trying them due to reports of their controls being very awkward, though people who got into them speak highly of them (the same is true of e.g. Daggerfall which has its adherents but its graphics made my head hurt.) But if there's one thing that fans of Gothic seem unanimous about, it's that Arcania is the weakest of the series. If you choose just one, don't choose that. Incidentally, Risen is generally considered the "spiritual successor" to Gothic 1-3: although it's not the same game world, it's the same team who worked on those games and it has a similar "vibe" to Gothic 3.

J'aime le fromage.