Abzu (I think some of the Journey devs made this)

It's literally Journey, except underwater and not quite as good. It's single player for a start, which is half the magic of Journey gone. And the underwater environments don't have the same beauty or variety as the desert/caves/mountains of Journey. Swimming isn't as fun as flying either.

I've actually always wanted a decent underwater game, I might give this a look.

It's on sale at the moment, or it was a few days ago when I bought it.

Yeah, it follows almost the exact same structure as Journey, level for level. I'd almost call it shameless.