I haven't used the NWN toolsets so I can't comment about them directly, but IME the Divinity toolset (which has an undeniably steep learning curve) sat somewhere between the TES Construction Set, which was probably the most accessible and easy-to-use overall (though it had its own problems such as being very crashy and creating very dirty plugins) and the Dragon Age Oranges Toolset which was just horrible even when you did figure out how to use it. And still crashed a lot. :|
NWN toolsets (1 especially, 2 less so) are pretty much the gold standard in accessibility, in my opinion. It had wizards for every tidbit, from NPCs to items to areas, and a very ergonomic and convenient UI, which made creating something simple - like a location populated by a few enemies, or an NPC with a functioning conversation - a matter of a few minutes. Of course, for something more complex one had to learn how to write scripts, but the most widely used ones - "give item/XP/gold", "change variable value", "update journal entry" - could also just be made with a wizard which only took a few simple inputs. About the one and only downside of it, apart from the limitations of the engine itself, was lack of transparent debugging feedback in the coding tool which made scripting a pain on occassion, especially for the newcomers into C++.
A testament to the powers of NWN2's toolset, which is a lot clunkier in comparison but also more powerful, would be the Baldur's Gate: Reloaded module, which is, well, a total remake of BG1 on a new engine and in 3.5 rules. They're working on BG2's remake at the moment and it's due to release sometime this year.
