This is definitely one of the lower-ranking ROTB toys for me. The transformation starts off good, as the legs and arms feel fairly intuitive and offer some cleverness, but the back/roof section is where it all goes downhill. As Gok said, the hinge is nearly impossible to move the first time and you feel as if you are going to break it (it is fine after the first time). I also found it very difficult to get the roof closed over the arms as there isn't enough clearance. I've tried it different ways and discovered that doing other steps in a certain order does help, but it never becomes easy.
I also don't like how lazy the Porsche approximation looks, especially toward the back. This may sound like a spoilt complaint, but we know they have the Porsche license now and the Studio Series Mirage is licensed. I just would've at least expected something a bit closer, even if not exact.
I will say that I do like how much closer the bot mode is to the screen model than the Studio Series (or at least compared to the renders of it we've seen so far). The only major divergence from the screen model is the head, which as Gok said might be a battle mask type of thing that comes and goes throughout the film anyway. I think it gives it a bit of a Depthcharge vibe myself. 
I will definitely keep this figure as I will display it in robot mode next to the Studio Series in car mode when I get it, but I'd recommend people skip this one and grab the Studio Series instead.
Looking to buy lucky draw Armada Prime and Diaclone Marlboor Wheeljack.