Everyone's experience will differ but I've gotten over 1300 hours of gameplay out of Valheim and most of those are solo. If all you want to do is beat bosses and get to the "end" of the game then you'll still get as much entertainment as you would most AAA titles with single player storylines. If you like sandbox type games where you can build things, explore, and generally make your own adventures, you'll get much much more out of the game.