Well, I'm really glad I did, because this is easily one of the best books I've read this year.
The basic premise is that the world (our world; the book is set in modern-day Moscow) is populated by Others -- people with magical powers. All magic comes from either Darkness or Light, and all Others are predisposed to one or the other. The Night Watch keeps an eye on the powers of Darkness, and the Day Watch monitors the powers of Light. The protagonist is a Night Watch agent named Anton, who gets sucked into an epic battle between Good and Evil. This all sounds like the set up to a fairly cut and dried story, but it's not at all; the book raises all kinds of questions about morality and free will and what it means to be human, and I found it to be fantastically complex. Anton is a great character, and the supporting cast is well-rounded as well.
The book is translated from Russian, and there are a few places where the wording is clunky or awkward, but overall the language is pretty seamless. Given that the prose is smoother than several books I've recently read that were written in English, I find it hard to complain much.
Anyway, definitely recommended. Now I'll have to pick up the other two in the series.
One funny thing: you all may remember that I recently read "Twilight" by Stephanie Meyer, which is a vampire romance. That book left a bad enough taste in my mouth that I had to reread a far superior vampire romance to clear my head: "Sunshine" by Robin McKinley. So when I opened this book to read a prologue in which a character is attacked by vampires, I almost groaned -- "here we go again..." Not that I mind vampire stories, but here I was hoping for something different... fortunately, ahough there are vampires in this universe, they're a really minor part of the story!