In many regards it's not terrible, but it's also not remotely good. Installs that take 20-30 minutes (infinitely longer if the game is larger than 2 gig), horrible download speeeds from Nintendo servers, a joke of an account system, a slew of ports that are worse than versions on 7 year old consoles, and 2 games from Nintendo that don't really do anything to show off the supposed power of the console. I can't blame anyone that's let down by what's being offered straight out of the box. Outside of Miiverse, there's not much to cheer about. They can't even get demos on the store. If the next Xbox and PS come out this deficient in so many ways, they better get ripped to shreds. People tend to rip Nintendo less simply because we've learned to have incredibly low expectations (hardware-wise). If Microsoft's next release is like this, the noise will be deafening.
On the upside, it's not like things can get worse. I expect a performance patch for the general OS. Opening settings etc shouldnt take this stupidly long to occur. But sooner than that I expect a patch to fix the netcode that's causing the entire Wii U to die when communications with Miiverse go wrong. That should never happen, and I wonder how many people will be getting their Wii U's "fixed" because they think it's the hardware messing up. What will never be fixed (imo) are the slow installs, the lack of achievements, the bad ports, and the inept account system. All reasons why people like me only buy Nintendo consoles for Nintendo-developed games. Not an insult, just a fact of life.
Nintendo fans can lament the criticisms being lobbed at the Wii U/Nintendo(part of being a Nintendo fan), but it's all fair imo.