I've noticed that most people don't include the following:
What type of Wii or Wii U console they are using and the region. Some games work on one Wii but not another or they work on a Wii but not a Wii U.
Is the ISO full or optimized and the region.
Are you using any special settings like MCEmu or force PAL?
If using a full ISO have you checked it against the known hashes?
What controller are you using as I've noticed some games are picky what controller you are using like Resident Evil?
Did the game ever work fully, if so what was the last revision it worked on?
Are you using a loader or launching
Nintendont via HBC?
Are you loading the games from internal SD slot or USB?
If USB and on a Wii U, are you using a Y-cable to give the HDD extra power?
If using MCEmu, what card size are you using?