I know there was initially some issues with the Wii U freezing early on in its release. Since a major firmware update, I have not had any problems with my Wii U freezing at all (although, I never really had a problem with this to begin with). It was only recently I really started having a major problem with my Wii U freezing, and I decided to post about this issue ALONG with the FIX I have found to the issue! 
The problem started after I bought a new harddive to expand the memory of my Wii U. I made sure to get a harddrive that was recommended by Nintendo on their offical website and listed here: http://en-americas-support.nintendo.com/app/answers/detail/a_id/1359/~/what-external-storage-devices-can-be-used-with-wii-u%3F
After the initial set-up, everything worked great. I had no problems moving all my large files and downloaded games to the external storage. The problem began after I was done playing Mario Kart 8, when I would try and return to the Wii U menu after playing, my whole system would freeze. I had no choice but to hold down the power button for 4 seconds to force the system to shut down. The problem seemed only seemed to start up after I added the new harddrive to my console, and only when returning to the Wii U menu after playing Mario Kart 8. For a while, I was confused and worried as to why the freeze would be occurring. I always made sure to take excellent care of my system, and was even using a recommended harddrive.
Then, one time when I was finished playing Mario Kart 8 and was returning to the Wii U menu, I heard my external drive make an odd noise, as if it was powering up. Of course my console froze as usual, so I decided to re-start everything and look at my game data. I realized the save file for Mario Kart 8 had accidentally been left on the Wii U memory, and not transferred over to the external drive. After a long gaming session of Mario Kart 8, where no data was being read from the external drive, it must have caused it to go into a "standby" state, and having to "wake up" the drive when returning to the Wii U menu seems to cause a freeze. So, I copied all my Mario Kart 8 data to the drive to keep it active during gameplay, and sure enough the freezing issue seems to be resolved.
If anyone else is experiencing a complete console freeze when returning to the Wii U menu AFTER extended gameplay, try making sure all your game saves and DLCs are moved to the external drive. This might correct the issue!
Cheers!
Message was edited by: SCOTTBOLGER
