Personally i think the dialogue is excellent for the sole fact that it is very informative. The story behind specific quests are always explained in great detail and if you keep asking questions i feel you can really learn all the details and specifics of what is going on. In other games, you just do what the quest giver tells you to do and thats it.

If you just read the dialogue, it isn't that bad. It is pretty linear, more like Morrowind or Oblivion then Fallout. However some of the voice actors in Gothic number 1 are just funny...unintentionally. the voice work goes from bad to mediocre, I haven't come across any really *good* voice work yet. However the dialogue is written as pretty run of the mill "gothic fantasy" style, mixed with oldish and newer terminology.
The biggest selling point of the game is that it is only six bucks, open world, and is a fun and deep RPG. The dialogue may not be the best, but there aren't many other games that will give you more bang for your buck. (Luckily alot of those games are right here on GOG ;))

I'd say Diego's and Gomez' voices are outstanding!
I have yet to come across unintentionally funny dialogue, myself, so it must be a matter of perspective. I also don't think I understand how Gothic is in any way linear. You can change the entire dialogue and sometimes the entire story depending on what you say to certain NPCs, with the exception of altering the main storyline.

Maybe I have a different standard then you, but I think Gomez's and Diego's voice work is merely adequate. I mean it's not bad, but it's not the best. Reminds me of early Anime voice work. But like you said, it's all in the perception.
And what I mean is that you can't change the main story by dialogue choices; you can't influence the dialogue by what you say like many RPGS..or at least I have not come across that yet. (I'm not that far in to the game, so forgive me if I'm wrong.) It isn't like the fallout series, or even the more recent Mass Effect where what you say generally influences many many things.
That's all; it isn't really a criticism...just a design choice. Not every game has to have these massive dialogue trees that change the plot when you mention you'd rather save a baby then kill it. (for example.) I don't know about anyone else, but I am not looking for the same experiance in every RPG I play, heh. And these are just my opinions, whatever that might be worth ;)

I've honestly not found a game with a single voice actor I like more than Diego's.
There's quite a bit of cause of effect in the dialogue. What you say will affect the outcome of the game. Though it's true it's not as dynamic as Fallout, calling it linear is also an inadequate descriptor.

Really? Not another game with a better voice actor then diego? hmm.. Mass Effect comes to mind, Jade Empire, Neverwinter nights 1 and 2, baldur's gate 1 and 2..etc. I dunno I guess it is just a matter of taste because I just think it 'does the job.' Ah well, such is life I suppose.

I hated every minute of Mass Effect, Jade Empire's accents sounded fake, NN's dialogue was good, but after BG everything that was done in that vein started to feel worn. It came down to a combination of factors, Gothic's voice acting seemed to match the setting pretty well and rounded out an outstanding fictional world.
I didn't say Diego's actor was the best, I just like him the most. I'm pretty sure the same guy did Gomez, whose lines were always awesome even at their worst.
One voice actor I hate is that one guy who is in EVERYTHING. I don't know his name and I can only think of a few examples off the top of my head, but it's the guy who voices the TIE fighter pilots in Empire at War. I swear his voice has been in so many video games it's scary.

I love mass effect (and the star wars: Knights of the old republic games). Jade Empire did kind of sound fake, but I don't think they were going for authentic chinese..I think they were going for Dubbed over movie chinese accents. Like Action Theater on TV from the 70's.
I guess it is all in perception eh?

Star Wars: Knights of the Old Republic is my numero uno RPG. My favorite game. I just love Bioware for it.
And HK-47. Isn't it a best character in all video games?

I like both of them, though the first one is Superior. I liked how you had to kind of unlock HK47 in the second game, but the ending seemed rather truncated.
I cannot wait to see what bioware does with the old republic mmo.

You must of been really bummed out when Diego opened his mouth in Gothic 2, hehehe. Man i hate his voice in G2 the should of just had the same guy from G1 do the work..

Every time I hear Diego's new voice I feel like someone else has taken over his body and made him sound like an overacted cartoon character. The German version had the same voice actor for both games, and it's a real shame they couldn't do this for the English localisation.

German RPGs are an odd bunch, almost deserving a genre of their own, I think. See Amberstar, Albion, Gothic...