Group is fun but solo is totally do-able if you have a tolerance for grinding and lonely corpse retrievals. You just need a bit more sneakiness and tactics.

The monster spawning increases for multi-player games, The bosses and several other monsters are more difficult because there are no distractions but you can beat them all by yourself, for sure.

The one caution I will give you is this. Development is very slow so if you purchase, purchase in mind that what you are getting today, may be all you ever get.

That said, you should get at least 50 hours of gameplay just with what is there even if you are not a base-building architecture fanatic.

You can also jump worlds with a character (provided that's permitted by the world owner)