If you haven't played since actual launch, there's quite a few things you will notice. The game is noticeably less buggy and less prone to crashing. The food system has had an overhaul, as well as several new foods added. Mountains now have "Frost Caves" like the burial chambers in Black Forest or Sunken Crypts in swamps, with a few new mobs added in for such. The crystals we got for defeating Stone Golems now have a use. A new roof type and several other build items have been added, like windows. Loxen are now ride-able after you tame them (Previously, taming them wasn't really worth anything). A new troll-tier mob has been added to swamps, and a new blob mob has been added along with tar pits in the plains.

If you're more asking about the completion of new biomes, I'm afraid you're quite out of luck.

The modding community has provided content in leaps and bounds, however. and if you're set on getting back into Valheim, it's well worth looking into those. However, be forewarned that each minor update from the devs seems to break mods (not really the fault of the devs or the modders, but annoying nonetheless).

All the official updates considered, you're not really looking at much content-wise that would be different from your original launch playthrough, with the exception that you'll probably crash less often.