We rode yesterday, and as long as the car is moving it's fine, but when the line stopped (which happened several times) it gets really stuffy and hot really fast. When we were stopped in the Riviera station with the doors closed and the car not moving was especially bad. If you look in the stations they have fans blowing on the cars to try and keep the air moving but sometimes you get stopped where they do no good. Overall, I was impressed by the system, but I can see guests freaking out when the system stops for any length of time.