Rahman is very very director friendly. He is ever ready to go whichever the director wants, the story wants, depending on the kind of movie or the music you want, and within that he finds his niche. It is a constantly complementary process. At the end of the day he is not pleasing you, he has to please himself.
If you take 'Agni Natchathiram,' it is about two half-brothers and their emotions and those are genuine, which can be made into a very hard-hitting film just that it can be presented in an entertaining fashion. Similarly with 'OK Kanmani,' it is a genuine film; it is not a flippant film just for commercial purposes.