Valheim is a very good/well made game for what it has, the main problem with the game is that its too linear. What i mean by linear is that they're is not a lot of stuff to do between bosses and critical points of the game. Sure you can make an extra 50 bases, tame 200 wolfs, or explore the 8 biomes. What I mean is when you defeat a milestone boss you go in the same cycle over and over. Grind gear to fight boss, grind gear to fight boss, grind gear to fight boss, etc etc. What the game needs is more stuff to do in between those loops like how they did mountain dungeons. But some new mechanics like reforging, enchanting, randomly generated mini-bosses, new friendly NPCs, or even making your own village with NPC's. Yes I know doing these things is possible with mods but for the most part mods wont meet the main games quality (Except Epic Loot and LVL and Loot control).
Cant think of a conclusion.
Tldr : Add content in between basic gameplay loop (Enchants, Reforges, NPC's, Random Mini-bosses)
Source: https://www.reddit.com/r/valheim/comments/sva87s/what_valheim_needs_my_opinion/