So the Wii U specs themselves are nothing to write home about when you compare them to the PS4 and Xbox One right? Well what is so interesting about that, is the Wii U is still a Next Gen Console in terms of graphics in it's own architectural make up. The only similar aspects the Wii U has in common with the PS4 and Xbox One are it's GPU feature set. The tech specs suggest at DirectX 10.1 chip but the extra custom features inside the GPU that are not listed in the dev kit, give it all the visual effects found in DirectX 11 GPU's of today.
A reminder:The Wii U GPU is highly efficient and not based on "Power Hungry x86" like PS4 and Xbox One: http://www.nintengen.com/2014/02/wii-us-gpu-is-highly-efficient-not.html
Keep in mind that the Wii U MCM (Multi Chip Module) is designed like a Frankenstein, meaning that the GPU, CPU and EDRAM are put on the same module (not a hybrid APU mind you but all separate parts working on the same module) and data rate is extremely fast between all units when developed correctly, making for a very low power consuming console using less raw power, but able to show visual results similar to higher end systems by eliminating the overhead, kinda like the Gamecube but in a larger way.
Basically, this thing is well designed:
Then you combine this with Nintendo going with PPC architecture vs x86 PC architecture and the pieces start to fall together if you do some research.
Does x86 have the capability to be power efficient? Yes. The designs are improving and are much better than they used to be versus Power PC.
Are the PS4 and Xbox One doing that though? Not quite. They consume a lot more power in watts than the Wii U does by a mile, and they need to this because they support components that are built with PC architecture in mind; and any PC Gamer knows you need a lot of raw power to get the best results and the higher spec GPU you buy, the better CPU you need to even out the efficiency, or your PC will have performance problems like stuttering and slight skipping when loading a streaming area in a large level in a game. It's a never ending cycle for PC gaming, but it's kinda fun being able to upgrade without buying a whole new system.
This is where the Wii U has a surprising advantage, what what you say? Well basically the Wii U has potential completely untapped due to it's design and the PS4 and Xbox One have extremely limited potential due to their own designs. How? Those systems will not benefit as much as the Wii U from having the games built from the ground up on them because they will never be able to reach the pinnicle of PC graphics due to each of them having low to mid range modern PC x86 specs.
The Wii U has suffered from poor sales leading to last generation un-optimized code porting from old systems, however some developers like Shin'en, Monolith, Platinum and Nintendo themselves with the new Zelda have shown that with far less power consumption than the Xbox 360 for example, they can produce results that look significantly better than that system:
Xenoblade Chronicles X:
Zelda Wii U:
Do you really think the Wii U could produce graphics like these at a max 40 watts power consumption without some highly custom/modified/tested hardware? You simply can't compare the Wii U to a PS4 or Xbox One in those terms, they are completely different in just about every way except for the GPU features which all 3 can produce similar effects.
Developers also have a lot they can work with in terms of texture compression and optimizing on the Wii U which some have already said is off the charts. What the PS4 and Xbox One have the advantage in is giving developers everything right at the beginning, they have all the power (right now) to make games look great with not too much effort, whereas with the Wii U, they need to write new code, texture compress, optimize and basically do more work to get the same results and granted with the low sales of the console, it's not gonna happen and devs would rather just not make the game on the Wii U due to this.
I guess it's a good and bad thing, good in the way that Nintendo made the Wii U so efficient and solid with the low power consumption and cheaper costs associated with it, but bad in that for developers to get the most out of making games for the console, they need to write code directly to the hardware and not try to port down or port in general other code designed for other systems in mind for it.
The Wii U does not have "high specs" but it's not underpowered either, it's made to play games designed for the console itself. Wii U = Nintendo's Gamecube mentality in console development.