Reading this book was like pushing a locomotive through a sea of molasses. Updike is apparently known for his very heavy descriptions, focusing in and in on seemingly unimportant details (like the scenery), and 'Eastwick' is no exception. Whether this appeals to you or not will most likely determine how much you like it. Literary trifles aside, this is a rich, sex-laden novel with lots of social commentary and underlying meaning. It's almost nothing like the movie as well; the characters are spiteful, hypocritical and vengeful, the magic seems to have more symbolism, and Darryl's role is somewhat different.
One flaw I saw with the novel was the fact that very little happened with any consequence. The witches have affairs all over the place, people die, and magic is thrown around a good deal, but it seems more for the sake of getting a vague 'impression' of what's going on, rather than pushing the non-existant plot forward. Much of the consequences in this novel usually result in something being gossiped about, and then it's back to the sex and hyper-focused detail and narrative meanderings, and then more sex.
In short, it'll be hard to sit on the fence about this one- it's not a likable book, but it'll be entertaining and thoughtful if you want it to be.