I played it recently. Very good game (although mediocre ending if we're being honest). The thing they did really really well is that it's true exploration in the sense that you could complete the game very quickly if you've already played it, because the only thing you need to complete it is some knowledge that you discover by exploring.

For example there might be a wormhole that takes you to a different destination if you fly through it backwards. You're very unlikely to find that out by chance, but if you explore you'll find a thing that tells you (probably behind some other puzzle).

Great game.