Well, I will not start with telling about story as it will spoil the fun for the people who haven't seen the movie or will see in the future, but I can see it is already spoiled here.
1> But I have to start with story which is extremely interwoven together. Now a days when people talk about first half and second half which doesn't matter according to me. Story has all the elements be it fun, romance, drama and it has a classic desi Indian touch with it because movie is based in varansi which gives it a flavor with its crispy language, people, ethnicity. Its pleasure to watch reality in the movie when all the movies releasing are masala shits.
2> If music is given by A.R. Rahman there is no point talking about it. Mucic was flowing like butter.
3> Performances are best like characters are meant for them. Dhanush is awesome in his performance. He is a delight to watch. The way he delivers his dialogues is super cool and his accent has a roughness and his south Indian accent doesn't interferes with his Hindi accent. Sonam looks sober and does her part with full conviction, Supporting cast especially Kundan's friend "Murari" is fun to watch.
4> Dialogues has everything from catchphrases, roughness to desi gaaliyan of UP.
Overall, it is a very good film after such a long time as we don't come across these days in bollywood :)