To simply put it, Vettaikaran is a very very poor imitation of various earlier Rajni movies and has striking similarities to the plots in Badsha and Sivaji . While Rajni had the screen presence to carry even a crass movie on his shoulders, Vijay is pale and with such weak script, it is very difficult for neutral movie goers to sit through the entire movie.
The movie has generated enough initial interest due to the marketing efforts of Sun Pictures but whether it can sustain its initial interest is to be seen.
I am not getting into the story/plot/script since there is hardly anything new - normal good vs bad theory and the hero strong enough to bash an army of villains single handedly.
Unfortunately, the songs lack melody, there is not enough comedy, stunt scenes are thrust and there is nothing which makes you feel comfortable.
If possible, please avoid watching.