^^^^ All of the above. Over 1400 hours (all solo, vanilla).

It can feel grindy at times and as Brakxel points out, mods are available to address that if you don't care for it.

At present there are no difficulty settings. Later stages of the game can be pretty hard solo. Sometimes "too hard" in my opinion but doable. Or at least not so hard that I want to start using mods yet. Some boss fights can feel like a bit of a slog ... not super hard, they can just take a long time.

Originally posted by Veseljko:

...
Go alone, go slow and prepare to spend hundreds of hours.

Great advice!