Just the price , it has come down heaps from the GP Black 4 but I think $539 AUS is still too high should be same price as the GP4 Silver in the low $400's. It also has the new mini USB lead (same as the session) so your old leads won't fit to charge the camera. Not such a big deal for me as I have other cameras that use that lead but still a pain in the butt. All cameras will go this way as it is fastest to transfer files.
If you want to see some good comparisons between the gopro 5 , 4 & 3 check these 2 videos I shot on the weekend. The 5 is mounted down by the steering (port side of boat) of the outboard and the yellow Hydroplane , the 4 is facing backwards in front of the engine & the 3's are facing forward in front of cockpit & by the steering (starboard side of boat) All the sound is used from the 5 , I just dubbed it over the other vision. Spectacular footage. All the mounts were just stick on's that Gopro supply.