For some reason when I watch this film it always feels like Nolan never made it. I mean the cinematography and all the visuals are totally Nolan, but the overall feel of the film.
I think this is because Insomnia is the only film Nolan never had a major role in writing the original story.
If I were to list the Nolan's films I have seen, first-watched to most recently watched:
Batman Begins
The Prestige
The Dark Knight
Memento
Following
Insomnia
(and of course Inception about 3 times in the last two weeks).
I guess you could say that I was already well versed with Nolan before seeind Insomnia. Before actually sitting down for the movie I read the synopsis and said "wow, the guy actually has insomnia, he has his own demons to deal with, and it's a Nolan flick, there's probably some major twist or something in it." It's possible that after seeing every other Nolan film I expected too much out of Insomnia. I had thought maybe Dormer's lack of sleep will affect his work more than it did, maybe Finch wasn't actually the killer, maybe more parts of the movie were actually Dormer's hallucinations.
The overall scope of the film is, also, not particularly as large as most of Nolan's other films. The plot is linear, no twists, relies mainly on major themes rather than simple plot devices. I think this is the biggest reason why I feel Insomnia is the weakest film.
If she plays cranium she gives good brainium.