I specifically said I don't think you shouldn't review books you haven't finished.
Oh, I think you can: if you find a book totally unreadable, what else are you supposed to do? Not review it and let some other poor sap buy it without warning? Struggle on wasting hours of your life?
Obviously, you should admit that you haven't finished it, so that anyone going through the reviews can get a feel for what's going on. Lots of one-star-couldn't-finish-it reviews vs lots of five-star-it-was-fab reviews will at least let people know that a book divides opinions rather sharply.
Apologies for thread derailment.