Mission: Space will obviously be a simulator, but not the same design as Body Wars or Star Tours.
It is based on a centrifuge design. The capsules are at the end of the "arms" of the centrifuge. As it rotates, you are pushed back in your seat, simulating the launch of a space craft. Through some sort of slowing of the rotation and tilting of the capsule (I think), the ride will also give the perception of weightlessness. Will you be able to float your sunglasses around the capsule? I doubt it.
With any ride that spins you around an axis, nausea is an obvious concern. Through careful syncronization of what you see and hear with the rotation, in theory, nausea can be decreased.
The capsules seem to have been designed to be cleaned easily, and I have heard of the area that you unload to as being clean-up friendly.
While there will likely be many health warnings for the ride, I doubt it will require us to be in "great shape".
More about Mission: Space can be read at the links below:
http://missionspace.wdwmagic.com/space_pavilion_ridesystem.htm
http://www.therideworks.com/index2.htm
Some is speculation, some is less specific... But it helps get an idea of what it MOST LIKELY will be.
Ted