I will start with the negative first, What I have felt negative is caste related dialogues. Ranjith should try to reduce the caste related dialogues. Its not the first movie, each and every movie he is doing the same. Except that movie is fantastic and Must watch movie. Below my opinion about this fantastic movie.
One more rocking performance from Arya after Mahamuni. Arya is brilliant as Kabilan and this is definitely one of his top-class performances. Arya is an absolute delight to watch when he is inside the boxing ring. His physical fitness has definitely added more authenticity to the film. However, he looks a little lesser intense in some emotionally charged sequences. Pasupathy is an actor par excellence and he manages to fit into any given character. Pasupathy, as a mentor figure is highly impressive and it is a treat to watch him perform. John Kokken, as Vembuli, strikes well with the action moves. He doesn't have major scope to emote, but with actions, he scores full marks.
Dushara Vijayan, as Mariyamma, the female lead, is promising and it looks like Ranjith has spotted another talented actor. Dushara (as Mariyamma) emotes really well when she tries to strike a chord with her husband. Kalaiyarasan leaves a good impact with the limited scope that he gets. John Vijay did his best as anglo Indian. None of the movie, director use him properly. Its one of the best movie for him after Mouna Guru. GM Sundar, Anupama Kumar, Santhosh Prathap, and others play their part well. One of my fav role in this movie is Shabeer Kallarakkal as DANCING ROSE - what an extraordinary character and what a transformation by the actor to play the role. The casting equation is fantastic and due credits to Ranjith and team for picking the right set of actors. After you finish watching the film, it feels like all the actors have lived in their respective roles.
Santhosh Narayanan's musical score is one of the biggest strengths of Sarpatta Parambarai. His powerful scores during the boxing matches elevate the energy to a different level. 'Neeye Oli' is great.
Sarpatta Parambarai definitely deserves a watch and it will definitely make your time worth it. Watch it for the awe-inspiring dedication of Arya and the effective execution of Pa Ranjith.