After signing various NDAs, the developer first came into contact with Wii U when Nintendo setup a presentation to his team at their headquarter to explain the then-unannounced console's qualities. The first alarm bell rang when the presentation mentioned explicitly that Wii U was designed to be no larger than the original Wii and to produce no noise at all so "mum wouldn't mind having it in the living room."Needless to say, that meant minimizing cooling fans speed and size at the cost of reducing CPU speed.
The development team expressed their concerns to Nintendo's team who assured them that "low power consumption was more important to the overall design goals"and that "other CPU features would improve the performance over the raw numbers". Eventually, the team got their hands on the actual dev kit and found that all of Nintendo's clever optimizations were not enough to outperform Xbox 360 or PlayStation 3. As for the GPU, it was better than on PS3 or Xbox 360, but leagues away from the graphics hardware in the PS4 or Xbox One. Interestingly, that was not an issue back then since both consoles were not released yet and nobody knew what their GPUs would end up be like.
The development team also suffered a lot trying to write and test their code on Wii U's development kits. To kick it off, the team was not able to get the development kit to run and Nintendo was not able to help them until it put them in contact with another third party development team who suffered from the same problem and found a way to fix it.
With the development tools fixed, the team quickly discovered that compiling and linking their code was painfully slow even for minimal code changes. Hours and hours of development time were lost while waiting for the code to be compiled and deployed to the dev kit to be tested. Moreover the SDK was so poorly documented, the development team had to contact Nintendo's regional office to contact Nintendo Japan for explanation. "Any questions had to be sent off for translation into Japanese, then sent to the developers, who replied and then the replies were translated back to English and sent back to us. With timezone differences and the delay in translating, this usually took a week !"
After working around all that and getting their game to a playable state, it was time to add multiplayer features. And that's when the team discovered that Nintendo was having trouble setting up its Nintendo Network. The team had a conference with Nintendo seniors to discuss the Nintendo Network's state just to discover that nobody in Nintendo's network development team has ever tried Xbox LIVE or PlayStation Network and that they never expected the complexity of such a network. Nintendo Network was not complete right until launch day. The team had to develop their network code "in the dark" and hope that it'd work as expected at launch.
In the end, the team cleared all those hurdles and released their "generally well-received" launch title to lackluster sales figures. "Without going into detail it would be fair to say that the numbers we were seeing were less than impressive. In fact we would be lucky to make back all the money that we had invested in making the game in the first place, and although the management publicly supported the Wii U platform, it is unlikely that we would ever release another Wii U title."
Keep in mind that this experience was more than a year ago. Here's to hoping that Nintendo has managed to fix Wii U's toolset in that period.