Open world with "biomes"
There is a progression of areas but you can walk into the wrong area .. the game will not hold your hand much. You learn a lot with death.
Your character has skills that level with use but health and stamina are based purely on food you eat and how well rested you are. Food and stamina management are everything in this game so you will need to do some farming and stuff as well as a lot of mining.

Once you learn what to do you can find safe ways to get through the game and avoid death.
Death you lose 5% of all skills and drop what you were carrying into a tombstone you can recover.

So multiplayer may mean you have more hands to do the work but you also end up with that much more work to do. Single player is balanced well for fighting etc. preparation is the key to everything.

This is not an MMO there are no public servers. Servers are private and passworded .. but you can go into looking for groups or on their discord if looking for people to form a group with.

Good luck and have fun!

Story
Odin put his enemies in purgatory a long time ago but found out they were having a party there and we have come to give them a hard time as resurrected warriors.