A good OS and a LOT of good games (like, at least 7 of them).

A Zelda game that does not use motion controls or any other gimmick like that and hearkens back to the days of LttP.  

A Metroid that isn't just a glorified FPS like Metroid Prime and is more like Metroid and Super Metroid.

I'd say a good Mario game, but i'll be honest, I think Mario is unsalvagable. 

Final Fantasy XV, Final Fantasy VII, Dragon Quest XI and Shenmue 3.

Confirmation that all their handheld games going forward will be playable on the NX.

That would go a long way for me.

The Gamepad is similar to the Gamecube controller in terms of button layout (2 control sticks, 4 face buttons, 3-4 shoulder buttons) and the concept of the second screen is an expansion of the GC-GBA connectivity. Even Amiibo is just an expansion of the e-Reader.

The concept of Gamecube was to make a console that would get strong 3rd party support which they missed out on with N64. The concept of Wii U was to regain 3rd party support by making a console that was easy to port PS3/360 games to.

On the other hand, the concept of Wii was to make a console that was accessible to all demographics (gamers, non-gamers, children, adults, males, females) by offering an easy to understand controller and software in genres that werent well represented.

Before launch Iwata also outlined the idea of making a console where games didnt require huge budgets and 3rd parties could focus on making software with unique concepts. Basically the idea of Wii was to offer new ideas and they werent worried about receiving ports of the competitors devices.

Wii U is a Gamecube 2, not a Wii 2.

Maybe this time they do care about what third partys would like to have ;)

Its kind of late. Nintendo is walking into a new generation that is already 60 million consoles strong and most gamers have chosen who their third party allegiance goes to. Sony is wrecking things right now. All they can hope to do is sell more than the Wii U at this point. its not looking good. The Wii U is Nintendos lowest point in history and the incentive invest in a new console is terribly low when it comes to library. Nintendo wont give Nintendo gamers Zelda until next year so they can create dual launch  with the NX and Wii U. I dunno dude....the more I think about it the more I think the unthinkable...and that is on the console game end, Nintendo might have to go third party because their console presence for the past decade has been downright confusing from a hardcore gamer perspective. it seems like their only way to fight back to go complete casual like the Wii.

This goes back to the original question in the first post. What can Nintendo do to get one to buy the NX in the first year? They will have to shock the world like they did with the Wii, but find some way to serve both the casuals and hardcore equally (Which theyve had a hard time doing for a decade now).

All I'd need is assurances that there won't be any game droughts (even if they have no western 3rd party support) and they could do that by unifying their software libraries. If they did that, I'd have absolutely no problem buying the NX day one.  Like this gen, if you gave me the combined 1st/2nd party software output of the 3DS and Wii U on one platform, that would have been amazing.

That's the problem. Without third party a drought is a certainty. First and second party are good for sometime but eventually on a monthly basis you will start to see the gaps. Granted, plenty of quality games will be created but at what cost? This is the greatest question of all.

Thanks to the unified library, I'd say the NX is guaranteed atleast decent Japanese third party support as I highly doubt they're just gonna stop making the Bravely Defaults, Monster Hunters, Yokai Watches, and so ons. They've also been collaborating with them on Wii U titles which has hopefully better'd their relations. Things still don't look good for Western third party support, but as long as they give them no excuses hardware-wise I'm sure atleast Ubisoft will bite. Even without them I think between a unified Nintendo and Japanese third partys they can manage 12 games per year at the very least.