I finished the paperback of the translated Nightwatch by Sergei Lukyanenko, on which the movie (look down) was based. The link goes to Froogle by the way -- I don't shill for anyone.
The movie was a non-stop WOW -- heavy duty action, flash, and outright weirdness. The book is a little more mundane, more talky, but still full of wonder.
A big difference is that the book makes it pretty obvious the author is a role-playing game fan -- "levels" of sorcery, references to Jedi, and such, but that's not a problem, certainly.
The movie covers only the first part of the book, although there are some major differences in how things are set up, and the relationships between Anton (the lead), Egor (the young boy) and Svetlana (the woman under a curse) -- I won't spoil it, but the resolution in the movie is actually a little stronger, although it burns some of the later stories in the book. Some of the things are explained a little better: Licensing vampires to hunt has a balance -- the Light are permitted to heal, to help to cure. Everything is perfectly balanced in the Truce between light and dark. The morality of this -- why can't light just do good? -- is the primary struggle for Anton.
A few of the scenes from the movie are straight out of the book and make a bit more sense: Zabulon/Zavulon sitting in the apartment where the Light are trying to figure out what to do about Svetlana's curse is nearly letter-for-letter, and makes more sense when they describe that the Daywatch is always permitted to have an observer when the Nightwatch has a field operation. Anton's sad, exhausted mood is very well captured from book to movie.
It's an entertaining read, good beach/plane reading. I'm looking forward to the second volume (due translated in January), and the second movie (which has been out since the first of the year in Russia, no word on the subtitled version for us here).