Good acting for me, when a person is believable.
While I do appreciate when over the top film acting is done well in the context(aka Kareena in JWM, Ranveer in Padmavat, Deepika in CE, Sallu in Dabbang, Ranbir in APKJK, SRK in Bazigar/Darr and so on), but good acting IMO is something which is done in a simple yet believable manner. But when someone is believable, like one example watch Udaan and Ugly, and watch Ronit Roy, that is a top class performance, where an actor has taken few emotion(anger and insecurities) and build a brilliant character whose every move revolves around these characteristics, it is simply amazing. Or Vidya in Kahaani( vulnerablity and naiveness), Sri in EV( innocence, love lorn and self worth questioned), Kangu in Queen( innocence), Ranbir in Rockstar( pain), Shahid in Haider( insanity), Nawaz in Raman Raghav( insanity and psychopath), AB Sr in Agneepath( arrogance and vengeance) and so many others. These performance are so centered by few characteristic yet bring natural reaction happening everywhere. I think these are the things which seperates great actors with good, average and terrible actors.
And the most important thing for me is, about actors who listen. Very few actors, especially in BW know the art of listening.
As for versatility IMO is a very misunderstood word, people seem to confuse change of appearances with versatility. Hence you see somd people saying that Nawaz is not versatile, I find him supremely versatile, Faizal Khan was a remarkably different person than Gaitonde, Chand Nawab was a totally different character than Freaky Ali, Raman was a contrast of Liak, despite these all being similar genres and scenarios.
Same with Vidya, Irfan and Tabu.
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