The amount of usable storage space available on the Wii U is hardly sufficient.
Unfortunately, these figures don't account for the preloaded data that ships with the system. After formatting, the Basic Edition actually only has 7.2 GB of data available for use, with 4.2 GB used up by preloaded software, leaving only 3 GB available for downloadable games and save files. According to Ars Technica, 3 GB isn't enough for an install of NintendoLand, which is 3.2 GB.
In the case of the Deluxe Edition, formatting leaves only 29 GB available for use. After accounting for the 4.2 GB used up, the Deluxe Edition actually only has 25 GB of storage available for use, which is still a paltry amount for AAA game installs.
Thankfully, the Wii U allows for SD cards and USB hard drives of up to 2 TB to be used to expand storage. Unless you'll be satisfied with playing only smaller games or repeatedly deleting games off of your Wii U's hard drive, it looks like this storage expansion option is a must.