They're not like a Chrysler Stow-n-Go where the seats recess into the floor. The second and third row seats fold flat and even with each other, but they're elevated from the floor. Here's a picture of my 2015 with the third row folded and you can see about where it's level with the rear hatch.
I've only owned it for a month, but so far have been very happy with the rear compartment. It'll fit 4' wide sheets of plywood and drywall flat, granted the hatch won't close if it's 8' long, but that's easily tied down to a receiver hitch. The second row seat mounts on the floor have a bar on the left and right sides that a ratchet strap can hook onto.