I am interested in knowing what games on GOG have user made campaigns. For example Neverwinter Nights has a huge amount of user made modules.

What about the others, Arcanum for example, VtM:R?

I think Two worlds & Sacred would be too much to hope for but anyone got any thoughs.

(Game tweaks and a few added bits i dont care about im looking for full blown user made modules and campaings for single player.)

FarCry has some.

Is there just the one for M&M 3 or is it user maps too?

I'm not sure i understand the question... anyway, i cited only HoMM3 because you specified "full blown" campains (and that is In The Wake of Gods addon); otherwise every HoMM title available here has tons of user made maps available.

Same for other games: if we should also consider single missions than there's plenty for farCry, Duke3D etc..

WoG I've heard og, havent tried it yet though, What I meant was is it Just WoG for M&M 3 or were there campaigns.

I apologise for my phrasing im "Slightly" hungover still.

If you go to Arcanum's developer's site not only do they have a few official and user made mods and expansions but they've got the Prima strategy guide there for free download.

And the Arcanum strategy guide was probably one of the best ever written because 80% of it was a highly useful appendix.

Sacrifice comes with a bundle of user-made maps and an extra map editor.

Serious Sam not only has a level designer but a modeler as well - I used and made some stuff back when the game first came out. Seeing as the level editor and modeler were fluent and well done, i would bet that there has been a lot of user-made content for Sam over the years.

HoMM3 has a massive number of user-made single maps, along with maps that are supposed to be played as part of a series (thus being like a campaign). HoMM4 is similar in that there are also a huge number of user-made single maps, as well as maps tied together into actual campaigns similar to what is in the base game.

Other than the HoMM series Freespace 2 also has a large number of high-quality user-made campaigns (you'll need to grab Freespace Open for most of these).