1. LOAD TIMES
- of course, they are not as seamless as the PS3 and XBOX 360. This is an 8th Gen console for goodness sakes. I look forward for an update to resolve this issue.
2. SYSTEM STABILITY
- there are many occasions that the Wii U freezes or lags. Either because the games are just ports that have been rushed, or it's mainly the operating system. This also needs iimprovements
Personal Experience: I paused Assassin's Creed 3 for Miiverse, after posting, I went back to the game. After 1 second since the game played, I paused it again to post another thing in Miiverse. When I went back to the game, the system froze and gave off a never ending beep. I was forced to unplug it. This is the second time already 
3. IMPROVED WII U MENU DESIGN
- it just looks too bland.
4. CUSTOMIZATION OF MENU
- 'nuff said.
5. MORE MII DESIGNS
- 'Nuff said.
6. ON SCREEN NORIFICATIONS
- like a friend who has gone online and offline, new notifications, Miiverse updates, etc.
7. IMPROVED NINTENDO TVII FUNCTION
- It's still laggy, and it could use more content.
8. NINTENDO NETWORK ACHIEVEMENT SETTINGS
- Similar to the achievements in The Nintendo 3DS' Mii Plaza.
feel free to add more 
Lets get this post to Nintendo! Their system will be a boom with these improvements we desire!
God Bless 