The game releases in what 3 months? I don't see there being that much more to it, but we'll see!

Some here have put Splatoon in a similar light before and look where that got them. Not saying Arms is the next Splatoon, but I'm not gonna be surprised if Arms has more to it than at first glance. Again, this is Nintendo. They usually go by selling you on the concept and later pouring out more details prior to launch. It's been like that with BotW. Of course, it's zelda, but they first let you in on the open world concept starting at E3 and have just now showed more details on the story and such (and the release date of course). Same with 3D World. Of course there are a few exceptions like Smash and Kart since there's little need for introduction of their concepts, they'll start by giving you what you want (i.e., new tracks, new characters, new designs, etc.).

Because it's Nintendo is exactly it actually, they generally always show the most important thing first, being the core gameplay. It's actually MK8 that's the only recent instance of the core gameplay changing significantly from reveal to release. Otherwise, Splatoon, 3D World, Smash, etc. played pretty much no differently from reveal to final product, and I definitely expect that to be the case for a game releasing in just 3 months. Zelda is the exception as they didn't show gameplay on it's reveal. It's because I know this is what Nintendo does that I wasn't among those doubting 3D World and Splatoon. The gameplay in Arms isn't bad by any means but I don't think it'll be enough to outweigh the motion control stigma, it's niche genre, and possible lack of content.

I think Arms could be pretty big for Nintendo if they do some proper marketing (and by pretty big, I mean develop its own fan base and following)...
I certainly can't see it being the next Pokémon, but some quality commercials could do the Switch more favors than those awful NSMBU and Nintendo Land commercials...

Well, Pokken not only made it to Evo last year, but was also the 4th most popular game with over 1k players. I don't see Arms doing anywhere near that.

OT: Splatoon was Nintendo's take on the online shooter genre. Add their own twist, make it much more intuitive, fun and less about how serious and competitive it is compared to most in the genre.

Arms, could be fun and not serious. But is this really a "popular" genre? I only see it as a more complex Wii Boxing game. There are no other games to compare it to, but that one minigame. It could do pretty good, but this ain't shaking up any charts.

It's not a traditional 2D fighter, it's not some WWE knock-off. It's more of it's own thing, specially since motion controls haven't been used since Kinect.

It's too hard to tell if this will be a new hit for Nintendo. It'll all come down to how it sells, and at this point in time, it's too hard to make that call.

Though I definitely don't see it dominating Esports : P

Punch-Out! on the Wii sold over 1.3 million and had great reviews and that game didn't have a lot of content.

Splatoon had one multi-player map, one weapon and no single-player campaign when it got announced. And Arms releases in Spring 2017 which could mean May or June (5-6 months). It will most likely be May as Mario Kart 8 Deluxe releases in April. 

The Nintendo rep said he had played this game for months already which means that the demo isn't exactly the latest build of the game either... 

I don't think so. This may just not be for me, but Splatoon, I got it instantly and wanted it day one. This game is meh to me.

Pretty much this. Depends a lot on marketing... but since this is releasing in May or June, according to the release schedule, I think they might actually promote the heck out of it like they did with Splatoon. Btw, note that this game is releasing basically at the same timeframe of the original Splatoon.