So true...Everything in your post is what I wanted to say...Even a small scene where Shweta feeds him Ladoo when he comes back, he showed his unhappiness as though he does not believe shweta has become good...that small nuances that Zain or makers give to Neil's character are the USP. Zain just takes it to the notch higher...Naamkaraan is lucky to have Zain play this roles...on the surface people will not realize but if you see the serial completely, then you realize the expressions he gives...
For ex a small scene like "Tubelight ho tum and jhallii ho sum" When Avni was speaking her lines, Zain/Neil was giving expressions whereas the camera was far and it was in a way not required and they way he smiled and said "Bilkul Tubelight" has so much passion and Naughtiness.