There's a lot to like here: The plot moves fast and suspensefully, making it hard to put this one down. The female protagonist is interesting, educated, down-to-earth yet urbane and sexy. The male protagonist is evil enough not to make excuses for, yet the book challenges you to at least consider his point of view.
Most excitingly, this book gives an incisive observation of maybe the most important social phenomenon of the TV age: voyeurism. Written before the Internet craze, this book has become only more relevant since! It describes aptly the temptation of wanting to play god in the form of an all-knwoing observer, as well as the dangers of such hubris: addiction, the seduction into doing something the perpetrator would intellectually/morally violently disagree with yet feels strangely compelled to perpetuate. Ultimately, the book discusses the consequences of such behavior as the perpetrator resorts to criminal behavior to continue his game.
Granted, there are a few flies in the ointment: the premise may not be considered terribly plausible. Yet, I believe it stacks up well against the suspense of disbelief required in most novels. The ending, however, while symbolically quite interesting (the voyeur becomes blinded, tying also into the Oedipal theme which is one thread in the book) is ultimately fairly contrived. Even more so, the final climactic scene, including the blinding, is just too far over the top to not teeter on the verge of the absolutely ridiculous! Mr. Levin could have definitely done a lot better there!
Despite these flaws, I still rate this one highly. If not taken all too seriously, this one's one satisfying ride!