Okay, back from a 4 day trip to WWoHP and have been through FJ several times. I'l try and add more stuff to other people's report.
We're a family of 4; me, DH and 2 kids, 5 & 7. Only I was able to go through the FJ which completely bummed DH out. He couldn't fit in the test ride at the top of the line because of his biceps and chest. Too wide. When they brought the harness down, the attendant said you had to hear 3 clicks as it goes down locking you in. They could only hear one click, and that's with DH trying 2 different days with different attendants, pushing his breath out and pushing back into the seat as far as he could go. So he ended up in the child swap room with the kids.
When you go through the castle you'll see a golden Hippogriff, past by a classroom door labeled Potions Classroom and if you listen closely you'll hear a lecture going on. You're literally going through a dark dungeon below the castle with "torches" lighting the way. Past by a wavy mirror, 2 portraits with a guy going from one to the other where there are people cheering on a quidditch match, past by the fat lady singing waving you on by, into Dumbledorf's office with him talking to you. The room is large enough to traverse back and forth several times still in that room while in line but I don't remember what he's telling you. Then you end up in a larger room where Hermione, Ron and Harry are whispering hidden in an invisible cloak. They eventually appear, and if I remember, they are trying to tell you that you are smuggled in and will be going with Harry and Ron on a journey where they'll bring you to a quidditch match. You'll be put on a broomstick and you're to follow them. Then you get to the front of the line where they'll start to separate you, directing you to the test ride for a body fit or the child swap room, single rider line or go on ahead, or the exit if you're just there for the castle tour. I ended up in the single ride line all the time.
Think of the ride as if you're Jane in a King Kong movie being held in King Kong's hand and that hand is swinging around and he's holding on by his feet on top of the Empire's Building and the other hand is swatting away at the airplanes. You're enclosed snugly. You hear a loud whisper and it's Hermione saying look at me! You look up and straight and see Hermione on a balcony and she says a magical word, waves her hand and you're suddenly being lifted up and away.
You're out of the castle, flying up to a walkway slightly on your back and see Hagrid with a ball and chain, and the chain lock is open and he's asking if you've seen his dragon. Then you fall back till you're flat on your back and you're falling down and away from the castle and suddenly you're being chased by a dragon. You're twisting and being thrown here and there as the dragon suddenly shows up in your face, blowing smoke, you go back through I think the castle with the dragon flying parallel to you, you fly back out of the castle room and Harry's sudddenly there asking where were you and to follow him. Now here's where my memory gets twisted up. I think you're flying over a lake, then through a forest where the thumping tree narrowly misses hitting one of its branches over your head, huge bigger than me spiders are dropping in front of you and spitting water into your face, close enough for me to scream and throw my head back to avoid them. Then you're out of the forest, heading toward the quidditch match, Malfoy swoops in and sneers at us, mutters something about muggles and now you're in the middle of a quidditch match when suddenly dementors appear. Now you're twisting forward, being flung sideways, forwards and backwards trying to avoid them, dementors popping suddenly in front of you and "chasing" you literally in your face as you're flying backwards trying to escape them, and I'm screaming wishing I could get away faster, LOL!. I think we're being chased back into the forest, dementors everywhere when Harry pops up with his Expecto Petrolus! and a bright light appears and the dementors scream and disappear. There's a smoke that shows up with the face of a skull, maybe Voldemort? that fades away. You end up flying back into the castle where Harry's on the shoulders of quidditch team members and they're cheering you on, the next room is Dumbledorf and Hermione and he's telling you well done, then his voice follows you reminding you to pick your stuff up from your lockers.