Think of it as a 3D version of Buzz Lightyear with more repeatability due to each scene being different depending on what you shoot.
Here is the latest description from Al Lutz at Miceage.
Midway Mania attraction will open in June, 2008. Most of the operational and artistic elements of the expensive new ride have been hammered out, and it really is going to rewrite the book on what a Disney dark ride is. With an hourly capacity of just over 1,500 riders per hour it will keep the lines relatively short compared to the more traditional dark rides that only handle 600 or 700 riders per hour.
The basic plotline to this attraction is that the Toy Story gang has created a series of midway games for you to play, and they are all themed to their individual character. Riders will sit in rather traditional looking dark ride vehicles that have a cannon mounted on a rotating turret for each seat. The vehicles will travel through the show building and come to a stop in each show scene, where a different midway game is laid out for riders to play. The plan is to have a half dozen different midway games offered up to each car, with a bonus round at the end to determine the winner in each car.
After an animatronic Mr. Potato Head acting as a midway barker lures you in to play, you move from one game to the next during the 5 minute long ride. For instance, the vehicles would come upon Little Bo Peeps Balloon Pop where you play the famous water gun race found at most county fairs. That would be followed up by the Green Army Men Shooting Range with moving targets coming at you, or Barbie's Beach Ball Bash throwing balls into rings. A Frontierland-style shooting gallery and a Rex the Dinosaur Red Hot Dino Dash amongst lava flows and erupting volcanoes are also planned.
What has the designers most excited, and where the huge costs come into play, is the interactive elements and extremely sophisticated technology needed to pull all of this off. The riders would be wearing 3-D glasses, and the animatronics and some of the special effects would be controlled much like the Roz figure on the Monsters Inc. ride where specific lines and reactions are directed at specific riders. It all promises to be very impressive and WDI plans on offering up several "How Did They Do That?!" moments throughout the ride. Older folks may find it a bit too frantic, but much like Buzz Lightyear the kids will instantly take to it and likely outscore their parents on the first ride. With all of the randomization and individuality offered up by each show scene, it's also an attraction that is going to have immense repeatability.