The quest design itself doesn't stand out as neither particularly bad nor particularly good to me. It's pretty standard Piranha Bytes stuff, where you have a mix of fetching, fighting, talking, and have some options as to who to help and how to get things done. It is made more enjoyable by how you are rewarded, as in addition to the usual XP and gold rewards, you will often get reputation boosts and stat increases which are relevant to what you were doing. Overall, questing is quite enjoyable in Gothic 3 (for me).
With regards to exploration, it is not just that it's big and pretty. It is also very varied, and it has the same hand crafted quality PB games tend to have, with lots of interesting locations to explore, and rewards to be had. For me, it may just be the most enjoyable game world I have explored, and also one of the most memorable. I remember so many places in Gothic 3, each of which has a distinct feel. Additionally, the soundtrack is exceptional, and really elevates the atmosphere as you explore.
As mentioned, I think Gothic 3 failed mainly in two areas:
* Technical problems, in particular the extreme performance issues. I had decent hardware at the time, but even on very high end systems, people where experiencing extreme lag and very, very low framerates. There were also plenty of glitches and bugs, and some quests which seemed to not have been tested at all.
* Writing, especially when it comes to the main characters and quests. I still remember how let down I felt when I finally tracked down Xardas, who I thought had a lot to answer for. It was extremely anticlimactic. We exchanged a few lines and he gave me a quest. And Lee…what the heck happened to his character? Barely any dialog and then off to kill the king, which you could do without anyone seeming to care.
I also understand that people were let down by melee combat. For me, I usually don't find melee combat interesting, so it was easier to ignore how bad it was. The only PB game where I actually loved melee combat was Risen.
As a side note, Risen seemed to be a sort of response to the criticism PB received for Gothic 3. It was polished to a much higher degree, limited in scope, and largely stuck to familiar ground, to the point where it almost felt like a remake of PB's most acclaimed game, Gothic 2. I enjoyed it a lot, but in some ways, I missed the big, beautiful, ambitious mess that was Gothic 3.