Just finished Twilight Watch last night. Of the three books, it is IMO the best of them, though the best overall story in the sequence was probably the second story in Day Watch (the one about the Mirror).
This one not only brings us back into the head of music-lover Anton, but introduces us to some cool new characters like Las and also really explains what's up with the Inquisition.
SPOILER:
The only real problem I had with the book as a whole is a similar problem I had with the first book -- Anton always seems to know exactly what simple spell he should use to save the day.
END SPOILER
Technically speaking, the author overuses certain words and comparisons, though that may be due to inadequate English words existing and the translator having to use the same words again and again. (They say Eskimos have dozens of words for "snow", right?) Also, I think he (Lukyanenko, not the translator) relies too much on lyrics to communicate ideas in the story.
I also think this one, as opposed to the other two, Lukyanenko wrote for a worldwide audience, instead of a Russian one. Anton's internal monologue sometimes sounds more like there's an undertone of "Hey, Americans, this is what's going on in Russia right now and why".
Still, I really, really liked this book, and especially in the third story, there's an awesome moment where I actually -- out loud -- said "Ha! Ha! Ha ha ha..." Not laughter, more like the "aha" moment. It's always good when a book can do that to you.
I recommend this book if you liked the first two, and if you haven't read those, you should read them and then this one.