Not a success, but considering how low the 3ds sales have gone, it was a bit expected. I had my hopes it would reach around 700k, but well, every game sold bad this year on 3ds, they keep announcing games but the handheld is pretty much dead at the moment, unfortunately. Look at fire Emblem SoV, around 500k only, nothing compared to its two brothers. Pikmin around 300k, ever Oasis didn't even reach 200k, DQ8 sold minimal as well. Mario and Luigi is around 150k, Mario Party might also be struggling. Only pokemon managed to sell in the million category, but again, it sold much less than previous iterations.
I love the 3ds, and I'm going to buy games for it as long as it's supported, but in general, everyone already moved to the Switch.

I wouldn't call it a failure, but it hasn't quite reached expectations yet.

It stands at 340k with 9 weeks of data left for the year, 4 weeks of November, 5 weeks of December.
It just sold around 14k with the latest Global figures of Oct. 28th, which was actually slightly up from the week before. I think that's an encouraging sign.
Assuming it sells an average of 14k for these last 9 weeks, that'd put it at around 470k.
I think it can reach 600-650k, if it's close to 500k by the end of the year, maaaaybe 700k.
If it can get around that range, than I think Nintendo will be satisfied.

If Prime 4 sells well, then the series will probably see another 2d game, this time with a new story/setting.

I think people prefer new games to remakes of really old ones. A lot of people speculated Nintendo would make a remake of a Link to the Past, but then they announced a direct sequel to it. That game sold very well because it was a NEW story and sequel:

3.35 million to the originals 4.61 mill sales.

Original Metroid 2 made 1.76 million, remake may make 500k lifetime.

It's clear that fans want direct sequels set in the same art style and world rather than just making a game, at least to me. I didn't buy it, but I would have had it been Metroid 5.

I think anything released on the 3DS is going to have low numbers at this point...

Wow, it really sold that much WW?

Metroid really is niche nowadays isn't it? The first 2D Metroid sold over a million units.

3DS games don't need to do high numbers to turn a profit or break even. Etrian Odyssey IV sold under 200,000 copies but Atlus keeps making more games.

It was 340k in October, we are now in the middle of December so its probably closer to 400k. Is not a succes nor a failure, it's still the 2nd best selling game of 3DS out of all the games released worlwide for the system in 2017, so its relatively low numbers are only a sign of how fast 3DS is dying and not a sign of a lack of interest in the franchise. In any case, as great as the game may be, it doesn't seem like the kind of expensive game that needs to reach a milion to be profitable, so once it reaches 500-600k I higly doubt is gonna make them lose any money.

Also... should we really trust VGC numbers when every fucking Switch game is criminally undertracked? Just saying.

They have Switch Breath of the Wild at 4.2M for October 28th on Switch, even though we already received official sales numbers of 4.7M for September 30th.

Success is relative. How well a game sells on an old console as a remake is a bit different from what a new game should sell.

Plus think about Fire Emblem: Awakening needed to sell 250,000 units to not be cancelled. Think about it.

That's mostly because of digital sales though.