My visit to MEPS wasn't fun, but it wasn't as bad as I expected it to be.
The first stuff is done with the guys - hearing, vision, blood work. Then they split us up. When I went there were only 5 girls vs about 50 guys. I was the only officer applicant in the group - most of the rest of them were high schoolers. The first thing we did separately was urine sample. The woman in charge of us was supposed to watch us give it to make sure there was no tampering, but instead we just had to leave the door to the stall open. We also couldn't wash our hands until after we had handed the sample over (gross!!). Then we had to change into paper gowns and we waited forever. One by one we talked to a doctor and then were checked out fully - it was a guy, and it was really uncomfortable for me, but I figured it could be worse. After all of us were done we had to do things such a duck walk, hop on one foot, twists, etc to show that our muscles worked properly - this was done wearing only bra and underwear. And then we were done

Overall, not particularly pleasant, but if you expect the worst, it will be okay.
Definitely bring something to read. You have to store any bags when you first get there, but you can carry a book around. There is A LOT of waiting around. Good luck!!