more photos here as well
notice the different backbox design for the LE's
also the balls go from the shooter lane potentially straight into a ball lock
It looks like the Pro will be a damn good game as it is.
http://pinballhead.com/first-stern-the-avengers-pics/The main differences in the higher model:
Arrow cross over ramp - can let go
Thor drop targets - but you get the HULK main drop targets.
Hulk smash ramp - still yet to see how the ball plays with the ramp up but you still get the mechanical/moving hulk and magnet action.