So i played very rarely pc in the last 5 years. My fascination with pc gaming was always that in many games people created stuff that were more intressting (at least for me) then the maingame like in Warcraft 3 custom maps. This are the things i am most interested, overhauling the whole game to a whole new game.

The only reccomendation that i got from my friend was Neverwinter Nights 1 and 2 because he sayed they are many modules which are very high quality and fuction the way i descriped, pretty much new games. Would you agree? Also what else in that direction can you recommend?

Thanks

Check out this thread that I created a while ago but then sadly neglected because I was swamped with work.

I like the kind of games you describe, too.* My favorites are Neverwinter Nights (so yes, I agree with your friend, at least for the first game), Unlimited Adventures (included in Forgotten Realms The Archive Collection Two) and currently also Fight the Dragon (Steam only, sadly).

And I really liked the total conversion Mod Nehrim for TES: Oblivion. So far it's the only "Elder Scrolls" game that kept me playing all the way through it (120+ hours). The beautiful thing about it was that nothing was random, all the areas were handcrafted and diversified in some way, so exploration was really fun. And it's a bit more like Gothic, no level scaling on monsters.

* EDIT: Just to clarify, I'm mostly talking about games that allow for creativity; most modules I like don't turn the games I mentioned in entirely new games, they just make them more interesting (better stories, better level design, partially better graphics, that kind of stuff - not necessarily change of rules). But especially for NWN there are some modules that also try what you're looking for (Soul Shaker is one that comes to mind; I never played it though, as I don't like reading rules. ;) )

Strongly agree. also I recommend Mount&Blade: Warband. This game also has many quality mods.Look at the link

Kerbal Space Program :)

ToEE
Arcanum
Fallout 1&2
Morrowind
All newer bethesda games
Mount&Blade-s
Europa Universalis 3, HoI3, Victoria 2
RCTW
UT04
STALKER-s
Xenonauts
Sim City 4

Doom 2 and Quake had (and to some degree continue to have) a lot of stuff made for them.

Edit: So does Duke Nukem 3D, though it's maybe not quite as loved as the other two.

I think the TES and Fallout games come to mind there at first. Dragon Age Origins should be good, too. Also a totally different genre, I think Cities:Skylines fits the bill, too.

Though talkinig about Warcraft 3 custom maps, while I haven't tried it myself, I think both the sc2 Arcade and dota2 should have some you seek and both are totally free.

There are far to many modding sites to list each here, it depends on what you want/like. I would suggest you visit:
moddb.com
nexusmods.com
These two have a vast selection on many games, of mods. Then there are game specific websites which you can find by googling, sorcerorsplace and gibberlings3 for Baldurs Gate, neverwintervalut for Neverwinter nights for instance, not to mention doom ones, dungeon siege etc.

Baldur's Gate series has a very active modding community.

FRUA
Heroes of Might&Magic games
Age of Wonders games
Doom
Duke Nukem 3D
Unreal, Unreal Tournament
Dungeon Siege (Lazarus and Ultima 6 Project)
Thief games

Doom (2) keeps getting amazing new community creations every year. Recent hilights include Valiant, Sunlust, Back to Saturn X (two episodes), Doomed Space Wars and much, much more.