Linear cover shooter space sim! Grapple onto the surface of an asteroid with invisible walls to keep you from moving in other directions! Fly on the surface of the massive evil alien space ship and bounce into invisible walls keeping you away from certain areas!
Asteroid fields? Just like Star Wars, but they move at a certain set minimum speed to keep you going forward and get denser as you move left or right.
Third dimension? Too confusing, so all enemies will spawn dead ahead and you move dead ahead!
Let's be honest, FPS level design these days is awfully linear and basic.
A good space sim could be done with a console controller (basic controls like WC1, not like the later WC games, X-Wing, for FreeSpace) but considering the arcade push... *shrug* I doubt we'll see something in that vein.