Just took part in the soft opening tonight. Was very impressed. This is a seriously cool addition to World Showcase. While I'm certainly not in the target audience for the Kim Possible TV show, and in fact have never seen an episode, I still found this to be very fun and very, very cool.
I was able to play the Mexico and Germany missions. In the interest of not being spoilerish, I won't give anything of substance away. The game incorporates lots of new elements in the pavilions that blend right in with the rest of the theming. It also uses several major things that have been around since Epcot's opening day. The only way for a non-player to know that something is part of the game is to actually see the element activated by the Kimmunicator. In fact, there were several times when nearby guests were surprised by what was happening and asked what I was dong. Some things are very subtle, while others are a little bit grander.
To answer some of the above questions, the Team Possible CM chose both of my missions for me, but I think the system default is random selection (could be wrong). I got my initial KP Fastpass in Innoventions at around 6:30 for a mission starting at 7:00. I didn't have to speak to any World Showcase CM in the course of either mission.
My only complaint was that the Kimmunicator's speaker was a bit too loud for my liking, and I don't think the volume could be controlled. Also, the buttons on the Kimmunicator I used for my second mission weren't 100% responsive all the time, but it was still definitely usable. All in all, I would rate this as not-to-be-missed, and look forward to trying all of the remaining missions.