Took the OAR a few minutes ago, so I'm going to try and get this down fresh in a sort of stream of consciousness style, then edit it later.
Math
Rough. Lots of complicated time consuming equations, some direct (e.g. (-4) - [-4(5-2)(-3) {-3[(9)(4)] -4}] ) and some built into word problems. It wasn't so much difficult in a lot of ways as much as it was frustrating. I felt like I was eating a big time crunch because a lot of the questions seemed to take a long time (and were not easy to reverse engineer with the available answers). It cut me off four minutes early.
Reading
Much harder than I had expected. I read something like 6,000 pages of material a week and have never struggled with reading comprehension, but I had trouble with parts of this. As other have said many questions seemed lifted from regulation books, and many answers were right but not perfectly accurate. It took a fair bit of rereading to confirm which fit and which did not fit, and even then I felt like there were a couple possible answers that really were dependent on how you read a single world. One in particular that jumped out surrounded child /spouse abuse and how preventing it (because it hurts readiness and moral) was the responsibility of commanding officers. One answer choice included something about how "officers shall prevent child / spouse abuse". A lot of that answer felt right, but shall suggest to me that it was an absolute, and I went another direction on it. I ran out of time here.
Physics
I felt like I got smeared across the pavement on this one. I'd focused my study around formulas for pulleys and leavers, circuits, electricity, leavers, edges, pendulums, and so forth, but neglected conversion rates for forms of energy and paid for it badly. There were at least four or five questions that proposed a question in weights but asked for answers in energy that I completely guessed on.
I ate a couple gear questions (which moves fastest if they are all different sizes), but nothing on leavers and very few on electrical matters. No current and no voltage questions. No device identification or anything like that. Nothing on heat exchange. One question on atmospheric pressure. No questions on convection or conduction. One two stroke engine question I guessed on.
You only get 15 minutes for this section (or I only got 15 minutes), but I finished well before that. For most of these questions you will know the answer or you won't, there isn't a whole lot of work involved.
I ended up with an OAR score of 59, which was a little disappointing to me.
I felt like if I had taken the time study a little more (I put in maybe six hours in the two weeks before I took the test) I could have done much better, especially on the physics and math sections (which I haven’t looked at in four or five years).