Mop it up, are you talking about hardware specs, or hardware design? Besides the pin connector issues with the original new, Nintendo console hardware has always been reliable. Can't speak for handhelds though.
A little of both really. You already mentioned the NES, but the Super NES has pretty loose construction that makes it feel a little cheap and flimsy, and the controller buttons are squishy. These aren't a big deal though, and the SNES is probably Nintendo's best and most complete system, from a hardware standpoint.
The N64 has the whole cartridges instead of CDs thing, and other problems like no sound processor, a small texture caché, and other bottlenecks. Oh, and the analogue sticks that wear down from use.
GameCube has the small discs, and then the limited availability of the component cable (and later removal of its port). And the short cords compared to the competition (I know they're about the same as Nintendo's previous systems, but at this point in time that was getting too short). There's something I'm forgetting at this time...
Wii has the most problems, not just from tech specs, but also durability. A weak disc drive, and memory corruption wasn't that uncommon either.
I don't have a Wii U, but the current OS problems and the day one update stuff sound like things that would annoy me. There may be some other stuff that's yet to be seen...
I know I can't expect them to get it perfect, but that's why it would have been nice if they had released some revisions for these systems like how they have with their handhelds to improve them and fix issues. The revisions for the NES and SNES came too late and removed features.
The original Game Boy and Game Boy Color were good, I can't think of any problems they had, at least ones that could have been solved during their time (such as battery life or colour screen). The original GBA had a dim screen to conserve power, even moreso than the GB and GBC, which was a huge problem. The SP fixed that though, and I can't think of any problems it had either, aside from the lack of a headphone jack which I don't care about. The Micro didn't seem to have any problems either, but a tiny handheld doesn't appeal to me so I never had one.
I never had an original DS but it did seem like a bit of a mess, a prototype, similar to the original 3DS. The DS Lite was good though, but it sounds like it has some durability issues as I commonly hear people have trouble with the shoulder buttons. The DSi/XL might have fixed that, but it was a lame stopgap system.
Now this isn't to say that I think other companies have done a better job at making systems, just that I'd like to see the quality of Nintendo's hardware match the high quality of their games. In most cases, I feel they don't.