First off, this game is awesome. Haven't felt like this since WoW release.
1-Variety, and extreme rarity of items. Have super awesome glowy weapons that look bad ass as hell where the only way to craft it is to find that 1 random cave on a random part of the map. The world is huge, force us to want to explore it all. This goes with super awesome food, items to customize colors of armor and banners etc…
2- a Fate system much like FF14, have random events with random bosses, some being extremely rare where super rare items can drop. Make fate bosses more rare than others on random parts of the globe where you only get alerted if you have an active campfire/workbench or are in the area.
3- Dear lord give me farming. Im talking the whole kabootle. countless plantable seeds, and the tools required to harvest them.
Bonus biomes – Rainforest, valley, desert, fjords, volcanic, tropical, deltas, tundra.
Source: https://www.reddit.com/r/valheim/comments/mcjdtd/name_3_things_you_hope_will_get_implemented_in/