With Matt Nava, the creative director of Journey fame in the mix, ABZU is likely to be something special, although it is highly unlikely to garner the sort of acclaim that Journey did, simply because Nava and thatgamecompany have set the bar particularly high. Translated roughly as "to know water," ABZU drops you in the deep blue sea to explore, experience, and interact.
As you might expect from Journey's creative director, the graphics in ABZU are not meant to be hyper-realistic, instead presenting the undersea world and its inhabitants with visually stunning style that dodges uncanny valley entirely. You won't mistake in-game footage for a real deep-sea dive, but the creatures and sights of the depths of the ocean certainly are more accessible this way.
While I was made to understand that there is some sort of overarching story within the game, the demo I played was purely experiential in its presentation. No objective was ever presented in the 20 minutes or so that I played. You started in the middle of the ocean, and you explored, investigated, and interacted with your surroundings, until you eventually happened upon the pre-designated "end of demo" area. The perception of the world is incredibly open at first, but once you've explored the vast spaces, you do start to notice the environment urging you in certain directions and along certain paths.
Interaction, however, struck me as the most fantastic part of the demo by far. If you see a sea turtle swimming past, you can press a button to grab on to its shell, and it'll take you along for a ride. The same is true of whales, which completely dwarf your character in size, as whales are wont to do, making the experience of hitching a ride all the more daunting - and rewarding - when you do finally commit.
There are hazards - sharks in particular - as well, though it was unclear from the demo whether they're just there to set you back by destroying your equipment (which is what I saw in an almost-jump-scare moment) or if they can actually get aggressive against you. Without that, we can't know what that sort of interaction might entail, but even just as a minor setback, it lends a sense of danger to the world.
Without knowing more about the various mechanics and story, it's a bit difficult to say whether ABZU will be a game that appeals to a broad gaming audience, or a title that caters primarily to those who are eager to appreciate the gaming medium primarily as a form of art, but it's certainly worth keeping an eye on as details become available.