This is a film with outstanding writing/screenplay - PERIOD! There are many kinds of films...some are acting centric, some are direction centric and some are visual centric, this is a writing centric film, which means it's screenplay, is outstanding compared to it's other aspects, and comes out as it's primary selling point and attraction.
It's been some time since the era of screenplay centric films in Bollywood began. I think, now it is flourishing.
Humor is good, subtle, novel, and is well written into the script. Some new, refreshing and skilled cast is also a plus point.
I have only one major complaint with the movie and that is it's abrupt ending. The ending is unexpected and surprising in the sense that at that point, it seems that the film will go on for atleast 15-20 minutes more. There is an improper closure, and viewers would have to use their imagination a bit to conclude things; I would have preferred a more proper closure to the investigation. But taking this aspect of the ending out, the ending seems well written with a good touch of irony.