Some of the nuances I have appreciated in NT's films are:
Paava Mannippu: The way NT writhes in pain when the acid is thrown at his face by MR Radha
Puthiya Paravai: NT bites his hand after realising he has killed his wife Sowcar Janaki with a heavy blow
Uthama Puthiran: The stylish manner he has essayed the villain role. Rajinikanth just followed him. An outstanding performance for the different shades of facial expressions with which he differentiates between the good son and the rogue one.
Baagappirivinai: When younger brother M N Nambiar comes back home from city and gives more attention to M R Radha and his sister M N Rajam, NT confronts him near the house well and gently chides him that he's ignoring his brother.
Vietnam Veedu: Can anyone forget his roles of Prestige Padmanabhan, a Palghat Iyer role, which he's donned to perfection.
One of his very best roles.
Ethiroli: A classic role of an upright man who succumbs to a moment's greed and is troubled endlessly afterwards for having taken T S Baliah's suitcase from the train compartment despite knowing the suitcases have been exchanged because of the train's movement, his suitcase going to Baliah.
Devar Magan: All the scenes involving NT and Kamal.
Paasa Malar: The scene where Gemini confronts him over workers' rights and the one where he overhears Savitri and Gemini in conversation and then wipes the tears with the pistol's barrel.
These are just a few scenes which I care to mention. There are
several such moments which we all cherish. Like someone has mentioned in this thread, my fav NT movies are also mostly bw ones.