I like reviews on amazon that have some of the plot in them, as amazon are so crap about posting the blurb or anything at all about the books a lot of the time. That said, I don't need a full synopsis or blow by blow account of the whole plot, just salient points to give me an idea if I'll enjoy it or not. It's not quite a "fine line" but needs to be just right don't want much do I? 
so as not to give too much away and spoil it.