Well, first of all I admit I’m not an UX expert nor UI designer, so I can design only trivial interfaces. Sorry.
I think Nethgui IS a pain because it’s a framework. Frameworks are a pain. When we develop within a framework we must obey the rules. This framework is VERY far from being perfect because it’s built on trade-offs. Moreover its rules are strict because it does not trust developers 
“We believe simplicity can still be powerful”, said Alessio about the NethServer mission.
So Nethgui is a tiny framework to implement simple interfaces, and - yes - it lacks documentation.
Because of this lacking I started to read the Cockpit Guide just to dream about how will be the UI in the future 
See also