I think we know a bit about it now. Specifically you have to get to the centre, you have to upgrade your ship to do so and you have to fight enemies that will otherwise kill you. You can mine resources and upgrade your weapons along the way. That the goal is to get to the centre means it has an objective that should hopefully satisfy those who hate truly open world, unending games.
Really though, whether this lasts 40 hours or 5 hours is not important - it's a new (and rather exciting looking) experience, something different to the many sequels and similar types of games that are continuously being pumped out these days. I personally cannot wait.