My review from my Trip Report. I'm assuming I don't have to warn about spoilers since this is a review thread.
It begins with a feeling of energy flowing through the "bike" and you, then the doors in front of you slide up to reveal what is a huge screen but to you it's a new "reality". I never perceived it as a screen, which really helped sell the experience.
You are quickly sent through some sort of portal and emerge within the viewpoint of a Avatar/Navi on top of a banshee. You are following a guide, another Navi on a banshee, and taken on an exhilarating ride through a strange yet beautiful world. The bike moves up, down, tilts forward and back and side to side to make you believe you are really flying. The glowing green seat you see in the photo above does expand and contract from time to time to mimic the breathing of the flying beast. It was flat out awesome! I was laughing, hooting, wowing, wooing, and more. It was also a nice long ride - almost perfect amount of time. You visit different landscapes and areas of the planet and have many thrilling experiences. At the end you return back through a portal and the ride ends.
So how do I rate this ride? It's the best I've ever gone on. I was never on Harry Potter so I can't compare, but this was just incredible. If you go in as a skeptic and try to figure out how it's all done, it will take away from the experience. At least for your first ride, buy into the experience. Believe your are really being transported into a Navi Avatar, stir up your imagination and let it run free. I promise you you will be blown away.
Congrats to Disney and the Imagineers. They hit it out of the park! The rest of the group unanimously felt the same.