Some of you more experienced Technic builders may laugh, but it took me almost three hours to construct this monstrosity and I enjoyed every minute of it. However, I am somewhat older than the average Lego fan, so I would not recommend this set to younger fans. It's just too dang hard to build. The instuctions are hard to follow and are actually wrong in places. This is the first set I've ever seen that came with a sheet of corrections for the instruction booklet. Or should I say instruction tome? The manual for this is bigger and heavier than your average news magazine. If I haven't put you off building it at this point, then you will probably like the set very much.
The way it works is that the arms fold in, locking under a spring loaded catch. Then the rear leg pivots up which rolls the entire spinal assembly forward; tucking the head away into the space in the middle. The front leg assembly then folds and locks in place. When the resulting ball is rolled, the red button on top hits the ground, releasing the front legs. The ball then rolls onto the legs, which causes the entire rest of the assembly to pop open. I didn't explain that well, but there's not really anyway I can make it clearer.
The problem is that the transformation is almost impossible to get right. Sometimes you roll it and nothing happens. Sometimes the legs flip down but don't hit the ground hard enough to trigger the rest of the change. Sometimes the arms stay locked up. Sometimes the head comes flying off and goes skidding across the room. This bugginess is all that keeps this set from being a 5, since, let's face it, the Destroyer Droid IS the single coolest thing in Episode One. Just having it stand there is pretty cool. About the only thing they could do to improve it is make the legs articulated, but that's really asking a bit much considering it actually transforms.
As for versatility, this set contains a lot of very basic Technic parts, so I would imagine you can make some pretty good alternate Technic models (the manual includes instructions for an AAT) but I haven't tried. It'd probably take me another 3 hours to take this thing apart.