Would suggest if you like chill openworld survival games that are amazing to play with friends. Building is also a big part of the game, so I would recommend the game to all fellow builders.

There is story elements, knowledge about vikings and hidden subtle references to viking mythology in the game, but there isn't a clear story that you would have to follow. Also if you don't care about the story it doesn't ruin your experience, you can just skip all the runes and just focus on the survival and progression. So I would say even if you are not interested in viking mythology or don't know about viking mythology this game will be interesting and you will learn basic knowledge about viking lifestyle even without thinking about it, for example how they built houses, what kind of foods they ate, which weapons they used etc.

Difficulty wise I would say this game is easy and relaxing most of the time, although sometimes it might be a little challenging, for example when exploring different areas for the first time (Dungeons, Caves etc.).
When it comes to fighting bosses, it really depends on how well you prepare. The first boss fight is really easy, but the rest of the boss fights you have to plan a little if you want them to be easy.

If you are interested about the time this game takes to be "completed" I would guess it takes 50-125 hours depending on how rapidly you are progressing, I would recommend taking your time and not rushing the bosses. If you don't spend any time on projects such as farms, cool houses and shelters you will miss a whole part of the game.
I personally still get new project and build Ideas that I wan't to create although I have completed all the bosses a while ago. But people have different opinions about that, I have many friends that quit the game when they had fought all the bosses, because the game became boring after they had "completed" the game.