I think there is a huge difference between what I consider "downvoting" (really, giving someone a poor vote due to personal issues that have virtually nothing to do with the review itself) and being voting honestly when a review simply wasn't of "extremely useful" or even "useful" caliber. Every review isn't going to get all "EU" or "U" votes, that just the way it is.
"Somewhat Useful" is a "C." Which means "average." I think, especially, when one is starting out, that isn't really a problem. When someone is learning a new skill, getting Cs is......well, average. I do really like when I see a new reviewer write a really great review. It shows me they put in the time, tested the toy completely, thought of alternative uses or at least alternative ways to solve problems with it, and put effort into the writing of the review.
I usually start reading a review assuming it is "helpful." Then I move my view up or down, based on the details, how accurate the data was, how imaginative the reviewer was, how much effort I felt was put into the review and yeah, syntax and grammar and spelling have about a 5% impact or more on how I vote. Text speak will usually cause me to not even want to finish reading the review, but I always do anyway.
I sometimes feel put on the spot when someone PMs me about a vote they felt wasn't "fair." Sometimes a review just was "average" (meaning a "C") or slightly below average and if I had anything specific to say about it, I would have in the comment section. It is NEVER personal, the way I vote. I don't care if someone likes the toy or not, it has no impact on how I vote. But, for me anyway, usually very short reviews, with little detail or little imagination or of course, improper data tend to get lower votes.
I spend an average of 2 to 3 hours (sometimes even more) writing each of my reviews. That isn't including any photos, or even editing. (I know people who have been here longer can write amazingly good reviews in a much shorter time, though.) I expect people to put as much effort into a review as I do to get a "helpful" review vote and a butt load of effort and imagination into a review to get an "extremely helpful" review vote.
I occasionally respond if someone PMs me, but I sometimes read up to 20 or more reviews in a day, and don't always have the time to get to my PMs in a few hours or even a few days. Chances are, I will get to them, but I do sometimes feel put on the spot when I am PMed with a "why didn't you give me a ____ vote?" If it was specific, I would have put it in the comment section. Sometimes a review just didn't hit me as an "extremely useful" review and I vote honestly and according to how I feel the review was written. Also, I don't always have the time to re-read every review I have already carefully read and voted on. Sometimes I will, but when it's a busy day, I can't re-read 20 or more reviews, looking for issues that may have effected the honest way that I voted.
Also, we are NOT required to explain our votes, if we feel we don't need to. Nothing personal at all. I never "downvote" in a retaliatory manner and I think most of us who have been here a while never do.
Sometimes the review just wasn't scintillating, sparkling or just didn't hit us as something someone spent a lot of effort on doing. I have to vote according to my conscience and often, simply my impression of the entire review in it's Gestalt. Sometimes, there isn't much to say about why a review was less than "extremely useful."