I was originally going to give it only 3, since her style didn't really shine for me, and the whole world that Atwood paints is revealed only in bits and pieces and therefore seems to contain a few holes while one is still busy reading.
However, a lot of loose ends are only tied up at the very end, which then requires one to "ruminate" a bit on what you had read before making an assessment of it.
I finished the book a while ago, and in retrospect, I think it's worth at least a 4 if not just for the chilling possibilities it presents.
In retrospect, I think I now appreciate the form and structure of the work more as well. It's very nicely tied tied together and rounded off at the end, and left me finally with a satisfied feeling that I never would have believed possible while still reading the "meat" of the novel. I think it's quite amazing how important the ending of a novel can be in leaving you with a good or bad feeling about a reading experience.
As for the scenario, anybody who knows a bit about how (even modern) theocracies are run, would know how apt and possible the scenario presented by Atwood actually is.
Although some aspects of Atwood's scenario might seem a bit far-fetched, one must keep in mind that this is a cautionary and exploratory tale; an exploration of what things might be like if certain events were to take place and if society then moved in the direction of the kind of society that Atwood paints.