Reasons I think the Switch will succeed:
1. The concept. I have been drooling about this concept since I thought about such wonders in the late 2000's. I think the concept is amazing and can't wait to get use of it Imagine going to a party and bringing your own Switch and people play drunk 1, 2, Switch? People say motion controls are dead, but I think the new tech from Switch (hd rumble, the joycon grip;etc) will give it some juice. People loved the Wii back then, and I think this is even better/more practical in our tablet/smart phone world.
2. The messaging. I used to work in advertising and I think the messaging here is fantastic. They have sold the concept as what it is, what it can, and everything very, very well. One of the things that made it obvious that the Wii U was in trouble was the bad messaging: "was it a new system? is it an upgrade wii? What's U?" I just didn't get anywhere from the start and Nintendo's advertising was never on the ball. It was also advertised as a kids toy first and foremost, while the Switch is advertised as a family/friend thing among all ages just like with the Wii.
3. The games. They cover a wide variety. You've got 1,2 Switch for casuals (this should be packed into the system I have no idea what they're thinking), Zelda for the hardcore, Splatoon for the softcore, Mario Kart, Pokemon in the future, b-games like Bomberman (hopefully it doesn't suck konami plz). You've got niche jrpg franchises. Another positive is that the pricing is scaled and not everything at retail costs 60 bones.
4. It just looks like a socially fun system. It looks FUN. That video you downplayed about the random guy who doesn't care about video games has it right. At the end he summarizes the system as something simply fun and social and less of a basement dweller thing where you play online by yourself in an isolated state like with PS4/X1. The fact you can take this with you is the icing on the cake.
Concerns that I have:
1. Pricing. If say Papa Game Fan and Little Game Fan both want a Switch either they're going to have to share it (a no no for handhelds) or buy two units. This is particularly worrying for Japan. In Japan the original 3ds sold at ¥25,000. The Switch is about an area of 29,000 Yen. The 3ds struggled in Japan and abroad until a price drop later that year. I think Nintendo has that covered though because they've STRONGLY hinted at a handheld only version of the Switch down the line. I think Andy's idea of a revision is extremely possible. I think that once the system hits the $200 dollar and 19,000 Yen range it will really start to take off and let's be honest, that kind of revision is only inevitable.
2. Online service. I'm glad that Nintendo is offering their online for free before they require you to pay for it in the fall. But whether or not it'll be good is to be decided. Here's hoping. I'm more worried about the communities aspect. I think Miiverse for instance should be more streamlined and easier to access, but then again that's coming from my experience on the 3ds and not the Wii U.
3. Price gouging and overpriced accessories. Nuff said.
Basically, price is my main concern, but I think that Nintendo will have no choice but to lower it when the sales start to dip eventually, which is inevitable, even at a loss. Would it be a loss if they sold it at 200-250? Who knows, but I think they'll do it anyways. I'm expecting a price drop within a year and a half of release.