To the OP...

I cant help with controller, I dont use that scheme.

Solo is fun ? It depends on if you are able to make your own goals rather than be told kill x boars for a bow, and y greylings for a shield etc etc.
Game is more like here the overall quest, kill the forsaken, you need to work out how to do this.
Game is linear in the way you take on the biomes... meadows - forest - swamp etc etc, but within that constraint its all up to you.
I play the game solo, and make my own goals for that session... today I am hunting for food, next I will mine some resources, I want to add to my home, I am ready to kill a boss... that sort of thing.
If you are fine making your own 'quests' then solo play will be fine for you, otherwise it will seem pointless and a chore.
There is no real time limit, you progress as you want, the raids get tougher the more bosses you kill but other than that you go as you want, this may or may be to your liking and this is the part that decides the fun part.

Hope that helps