My question in the title and are there any changes or losses of interesting features as the game series progressed?

That's a very subjective question, I don't think there's any universal answer, but here's my opinion:
* Gothic - my favourite of the series. Has a bit unique controls, but once I learned them, I consider them one of the best in this type of game. Three distinct camps surrounded by a barrier, overall a very hostile environment for a new player, but it's very enjoyable to climb the ladder in the hierarchy.

* Gothic 2: Night of the Raven - since this one is with the addon, it's way more difficult than the first game. Controls are similar, but with some minor changes. The setup is also familiar: three different factions stuck on an island. The beginning is also hard for new players, and you can climb your position within the faction as well. You will visit the area from the first game, so it's nice if you played it prior. Addon opens up new area of the island with two minor factions.

* Gothic 3 - I haven't finished this one yet (tried twice), this part of the series has some major differences compared to the previous titles and there are some problems with this one. The development of this game was rushed, therefore certain aspects seem unfinished, especially controls, which although simpler I consider them bare bones. This time the world is way bigger and open to explore and you don't need to join any faction, it uses reputation system, so you can work with as many as you want, but some quests will of course anger one group and help the other. I like it, but it has problems.

As for the rest of the series, I haven't played them, since the original developer (Piranha Bytes) lost the rights after Gothic 3, and later games have been made by someone else. From what I've read they're not very good. Prianha instead have created the Risen series and Elex. They now have the rights to the Gothic franchise, but the damage has already been done. We'll see whether they'll make a new one.

i liked gothic 2 the best, it has the best combination of graphics and gameplay. Gothic was ok, but just a engry level game to me. Gothic 3 had the potential to be amazing but was rushed and has many many problems. So, 2 then 1 then 3. Again, 3 had the potential, there is a whole lot i like about gothic 3, then again there is a whole lot i don't like about gothic 3, which cancels out the good stuff.

It looks like it's between Gothic 1 and 2 then.

For me it is definitely Gothic 2 without expansion. But that might just be a matter of taste. You have heard most of the features in the answers before mine, but the difference is that in my opinion: 1. the story feels more coherent and the voice acting does not have any strange differences in voice/pitch (this is at least true for the English version). 2. the gameplay feels nicer than in NOTR. 3. the atmosphere feels a bit nicer at least for me (but pirates is not really my thing, at least in this game). NOTR feels like it's just blatantly pushed onto an already nice game.