A little of both. A more appealing concept would have done better, but assuming their software output would have been the same thus far, it really wouldn't have done that much better.

Execution, of course, will come, starting now in Europe and in a few weeks in the good old USA.

Execution, basically it would be doing fine if not for the huge drought. Price and advertising are also factors but without games those are meaningless.

nintendon't do nothin wrong.

concept, since the N64 all Nintendo consoles had gaming drought and they never dip below 25k so often and so quick

The others were never in a situation where they had no system sellers though.

Concept, IMO.

Whenever a new console comes out, it is because it is addressing a specific problem or set of problems that need to be solved. The Wii-mote was the solution to a long-standing problem, accomplished in an original way. While the Gamepad has its uses, as the basis for a console, it is a solution looking for a problem. And one reason developers aren't working on it is because it doesn't solve the problems that they are having.

The execution, however, certainly didn't help.

A little bit of both, but mostly execution.

It was when they were being fed on the Wii craze when they thought "Ok now every console needs to be like the Wii and reinvent everything". That got us the 3DS (which they be salvaging) and the WiiU with the gamepad.

3DS 1st 6 month execution was bad, and then they saved it with software. That's what the WiiU needs right now. Compelling software to justify it's existence. I want to see Pokemon in 3D, I want Metroid WiiU with gamepad scan visor.

Neither.

The Wii U's major failing is the market comparison with the PS3/360. Your ordinary uninformed consumer walks up to the shelf and sees three HD consoles. The Wii U has the highest price and the fewest games. Bam: poor sales. And there's really nothing Nintendo could do about this, either.

Arguably Nintendo has failed to sell the Gamepad as a revolutionary way to play games, but even there I don't think so. Even if Nintendo had been pushing multiple major titles a month for the whole first year in a historically unprecedented fashion, the Wii U would still not look particularly appealing until the PS4 and XB1 launched. Even with titles, it's still expensive and lacks a used game market.

Execution first and foremost.

Delays resulting in further delays and losses of exclusive third party content lead to much lower sales than previously expected. Games are the main reason why people buy video game consoles, and they simply weren't/aren't there.

The concept is solid, but requires first hand experience to be fully appreciated. This issue is finally being addressed through Best Buy deals and the likes where people get to play the games and explore the concept without actually owning the system.

I agree with this wholeheartedly. 

Though I also think the execution suffered as a result of the concept. I don't think they can be seperated. With the Wii, simplicity and ease of use was key. Its like Nintendo, said, 'fuck that' and decided to hodge podge all previous ideas into a blender and voila la we have Wii U. I don't think off TV play is a big enough selling point. Its a convenience for some, but a non issue for most. 

Imagine Nintendo abandoning the NES controller concept for the SNES and instead opting to go back to Atari type controllers. That's what they've done essentially.