The content that is there currently can easily put you over a hundred hours (I've gotten to 500), unless you're the type of person who tries to race to the end as quickly as possible. I've played solo the entire time. Valheim is more enjoyable if you take your time and enjoy the journey. Carelessness will be punished, but it's not bad if you go slow, gear up appropriately, and do some problem solving or read some guides if you get stuck.

The game is not finished yet, and probably won't be for a long time, but what is there is is quite playable. I don't know which "less developed sections" the person above was referring to unless it's one of the three placeholder biomes that haven't been filled yet. The five main biomes that are finished play like a complete game with bosses at the end of each one.