To put it simply I have played Gothic 2 without the expansion a couple of years ago and I have greatly enjoyed it. So I am looking forward to play the expansion Night of the Raven. However, it seems that Night of the Raven is not an add-on but that it blends with the standalone game.
Does that mean that I must replay the whole game to access to the expansion parts? Since it is still fresh in my memory, I'd rather play only the new parts... Could anybody explain me how the expansion works? Is that possible to progress in the game by playing only (or at least mostly) the Night of the Raven parts?

Thanks in advance.

I recall it being blended in a way that I found difficult to figure out how to play it independently.

While I don't have the gog version I have both the original Gothic II and the game plus Night of the Raven boxes. Back then I had your exact same question, but I finally had to assume that I was being "forced" to replay the whole game again to enjoy the new content. Not that it was something painful to do, mind you. When Night of the Raven was launched on my country a few years had passed since the my playthrough of the original, so memory was shoddy enough to enjoy most of the quests and storyline again.

Unless you've just played the original (and all is too fresh in your memory) just start a new game with the expanded one. It's worth it.

In addition to what's already been said, it should also be pointed out that NotR greatly increases the difficulty of the rest of Gothic 2, so although you'll still be playing through the same Gothic 2 story the gameplay experience will be quite a bit different.

Thank you all for your answers.
I guess I'll just start again the whole game in a few years.