Firstly, if you are expecting a Christopher Nolan film, look elsewhere, this is the film where him and his brother have had the least input into the writing (none). He's just directing someone else's idea. Don't expect constant twists and new interpretations scene to scene, it's not that kinda film.
He has however directed the film very well. You follow a cop struggling under the weight of his burdens in a land where the sun never sets as he struggles into ever deeper insomnia caused tiredness. At every step of the film you feel his weariness and that is the films greatest fault. It's aim is to convey the insomniacs state of mind to the audience and it does that. But that involves making the audience feel burdened and tired, which is what happens. The pacing is slow and you follow the train wreck that the LAPD detectives career becomes all the way to the end. You hate the bright and cheerful villain (a fantastic performance by Robin Williams) and get every more depressed as everything closes around you.
It's like the Road, it's a great film, but fun is not the aim. You just want the sun to set