Let's be honest — the Wii U is going to be left in third place in technical terms when the PS4 and Xbox One release later this year. Nintendo's system simply isn't as powerful as Microsoft and Sony's machines, so it's reasonable to expect something of a graphical disparity between the platforms — just as was the case with the Wii, Xbox 360 and PS3.
However, Shin'en's Manfred Linzner insists that the console is perhaps more capable than people give it credit for, and that it actually offers considerable benefits over the previous generation of hardware. (Warning: The following quote contains more than its fair share of technical mumbo-jumbo.)
The Wii U eDRAM has a similar function as the eDRAM in the XBOX360. You put your GPU buffers there for fast access. On Wii U it is just much more available than on XBOX360, which means you can render faster because all of your buffers can reside in this very fast RAM. On Wii U the eDRAM is available to the GPU and CPU. So you can also use it very efficiently to speed up your application.
The 1GB application RAM is used for all the games resources. Audio, textures, geometry, etc.
Theoretical RAM bandwidth in a system doesn’t tell you too much because GPU caching will hide a lot of this latency. Bandwidth is mostly an issue for the GPU if you make scattered reads around the memory. This is never a good idea for good performance.
I can’t detail the Wii U GPU but remember it’s a GPGPU. So you are lifted from most limits you had on previous consoles. I think that if you have problems making a great looking game on Wii U then it’s not a problem of the hardware.
It's almost certain that we've not seen the best the Wii U is capable of yet — better looking games will appear as developers learn to exploit the hardware in new and exciting ways — but it's clear that some third-party titles on the system aren't pushing it enough. Hopefully as sales pick up towards Christmas we'll see fresh support from publishers and developers, resulting in a stronger indication of the console's graphical prowess. There's also Nintendo, of course — the company is sure to produce more visually stunning Wii U games as the years roll by.