How it felt, how it worked best, methods of use that could prove useful to my own uses, and clues as to whether or not it would fit my own anatomy and tastes. I'll sometimes click over to a reviewer's profile to see if we have any toys in common, and if our opinions line up on those, I'll find the review more useful to me.
(As in, actually useful to my purchase plans, not "useful" as in the voting thing. That would obviously be unfair.)
I wish there was a better way to measure vibrational pitch, rather than relying on people's subjective opinion and use of words like buzzy and thrummy and thuddy -- I think the accuracy of that is pretty surprisingly good, considering that some of those terms aren't even real words, but I'd love to be able to compare things more directly to my existing favorites with something a little more scientific, like a numerical value.