I think what's interesting is that it shows how much of a 'hired hand' Nolan was on this movie. It's a credit to him that it turned out so well considering how much he had to kowtow to the studio (he didn't even have final cut).
It's certainly the least 'Nolan' of Nolan's output, but it's an important film in his career because it proved how easily he worked with big name actors. It was Insomnia that got him the Batman Begins gig.
I used to intensely dislike Robin Williams as a performer but I remember walking out of the cinema at the time and thinking 'wow, he really can act'.
This is why Nolan succeeds. He is a master at protraying what he wants the screen and making it available to all to understand. He translates his vision so perfectly to the big screen. I know this is exactly how I felt when I watched Insomnia.
I wanted to make a film where night and day started to become confused. As you follow this character his perceptual distortion is increased, and you start to wonder whether you're seeing the whole picture and how much time has passed. So I wanted the audience to be floating a little bit by the end of the film.