Looks good, how big is the world in this game, can you explore the whole planet?
We don't really know at the moment. It seems to be endless - someone claims to have flown a huge distance across the surface and found no barrier. It could be planet sized, or just a flat plain with a skybox, but as it's still effectively in alpha everything could change.
The planet so far is static - always the same setup for every game - resources always in the same places, alien spawns always in the same places etc. This could be the pattern for the final game, or it might have randomization added - I don't know. It's not a voxel sandbox like Minecraft - more a scenario with variations like The Long Dark. Assets can be harvested for crafting materials etc, but the landscape isn't destructable.
The backstory is that there has been one Project Osiris expedition to the Gleise 581 system so far, and the gameplay takes place during the second expedition. There will be a plot of sorts I believe, as the devs say in the FAQ that:
"Players will be able to explore the planet, gain resources and materials to craft structures and equipment, manufacture vehicles and weapons with the goal of colonizing the planet. Players will come in frequent contact with the indigenous alien species (12 planned for Early Access launch) as they expand and explore more of the planet and – in time – uncover the dark mystery that hangs over Project Osiris."
Other planets in the system will also be open for exploration and colonization. There are two factions (both human) - the Earth government expedition, and renegades/separatists. They plan to have numerous playmodes including solo offline, private servers, and public servers (both PvE and PvP) but not all are working right now. Solo offline and private servers are, but there are a lot of teething problems. The alien presence can be adjusted by slider from zero through to insanely infested, but I don't know if this is just for the early access test phase. There will eventually be 4 character types, but at the moment you can only play as a science/exploration specialist.
It's still very unfinished and full of bugs, however it is pretty stable to play. It feels like they are up to the stage ED was at just prior to the end of alpha testing - starting to come together, but a lot to be added and fixed. The devs are very responsive and communicate frequently. There have been 3 patches since the EA release and they are adding some features suggested by the community. Release is planned for "2017" so that could be anything from 3-15 months away. I's say it has 6-12 months work required.
The devs are pitching it as something like a combination of The Martian and Promethius, and that's not a bad comparison. It has elements of Pitch Black as well. Gamewise a number of players have commented that it is rather like Ark in space.
The music and effects are good, and the graphics really nice. In fact some of the best I've seen in this style of game. Several notches better than any voxel-based game I've played. The alien and player animations are excellent - smooth and realistic. There is an interesting design tension in the game between open-world sandbox and adventure. It will be interesting to see how it all comes together, but so far it's quite impressive.