I'm going by Metacritic score.
XV is a "success" in that Square-Enix actually managed to ship the damn thing and make it pretty good. But I absolutely stand by my statement that this could likely be the worst game in the main series by nearly every objective measure we can think of (average critical score, budget, development time, sales #s).
Going by Metacritic score:
Captain America: TWS - 70
The Avengers- 69
Titanic- 74
The Empire Strikes Back- 80
Godfather part 2- 80
Avatar- 83
Shawshank Redemption (considered to be one of the best films ever) - 80
The Force Awakens- 81
Look, if people don't like something, they're well within their rights to do so. There are valid criticisms to be had regarding pretty much anything. But basing something's quality or success off a metacritic aggregate is problematic and inaccurate. For example, more than half of FFXV's reviews on Metacritic are between 100-85. The rest are mostly 8s, with a few outlying 6s. Metacritic's weighting system for outlet reviews is opaque and not understood; many questions have been raised about it, with no answers given.
Again, this doesn't invalidate whatever criticisms people may have about the game, for the most part; it's my GOTY and I recognize it's not perfect. Nothing is. But again, this is why most reviewers you'll meet HATE having to score their reviews, and HATE metacritic. It's heavily flawed and doesn't provide an accurate aggregate at all. I'd argue that if you liked the game, it succeeded. If you don't, then it didn't. Simple as that.
As for sales, well.....it shipped 5 million. That's what retailers bought. It's already made a ton of money for SE. Retailers base their purchase of games for sale based on preorder numbers and interest. They don't do that unless they're confident they can clear most of that stock. XV was Gamestop's most anticipated game of holiday 2016, and Nielsen had it listed as RIGHT below CoD and BF1 in terms of consumer anticipation. Here's now Nielsen broke it down in terms of consumer anticipation:
CoD: 96%
BF1: 96%
FFXV: 95%
That's pretty damn impressive. Now, one might say "I still hold FFXV as a critical failure (utterly ridiculous BTW) because of an 82 meta, FF should score better". Of course, that's not taking into account the MUCH harsher review scale levied by critics this gen, which is a GOOD thing. Deus Ex, Uncharted, Gears of War, FF, Fallout, Dishonored, Farcry.......these franchises are scoring a bit lower this gen. This isn't due to a dip in quality at all, but rather a recognition that too many games in 7th gen were handed 9.5s and 10s without a thought to very real issues present in these games. I don't think anyone can deny this. Issues such as framerate, bugs, glitches, camera etc. are no longer being given passes, and as a result, an 8 means something again. Did you know that last gen, pubs were reluctant to greenlight a new IP if they hadn't produced an 85+ metacritic game? Shameful. Last time I checked, 8.5 was a fucking DAMN good score. Someone on our podcast gave TLG 4/5 stars, which metacritic would consider an 8/10; it's his GOTY.
Anyway, I hope you see the point I'm trying to make.