Here is an in-depth side by side comparison of Assassin's Creed IV: Black Flag for Wii vs PC. Normally I would compare it to PS4 or Xbox One, but after seeing this comparison I wanted to spotlight the PC version. The Wii U version is very close to the PC game, all the detail minus some rain particle effects, a bit lower texture resolution and shadows. I have not personally seen a better job of porting to the Wii U yet. If you haven't picked up ACIV on the Wii U yet.
Amazon is having a deal to pick this up brand new for just $24.88 and used for $19.95, check it out here:
Link to Amazon page