Super Mario Run was also always-online for no reason, you couldn't play without an internet connection.
And it wasn't a particularly impressive game. There's no shortage of endless runners on mobile, and Nintendo didn't do much to differentiate themselves, so it's no surprise nobody bought it.
I think the always-online thing is a DRM thing. I could be wrong, though.
As for the game itself: I've played it, and it's a pretty decent runner with the physics of New Super Mario Bros. Wii/U, but it's just not the same as the more full-fledged games. It's fun to pick up and play, but not groundbreaking or particularly special.
I was really disappointed by that choice. I had wanted to buy it for a plane trip I had shortly after it came out, but being online only, they lost that sale.
It seemed like an anti-piracy move because the game didn’t naturally need to be online. But I never thought iPhone app piracy was much of a concern.
The online-only aspect of it killed it for me. I lived in an area with spotty cell service when it came out, meaning a game that would otherwise be a great time killer was unplayable due to the DRM.
And it wasn't a particularly impressive game. There's no shortage of endless runners on mobile, and Nintendo didn't do much to differentiate themselves, so it's no surprise nobody bought it.