4Game

Explored like half of the world and it becomes repetitive with no incentive after having discovered all biomes.

What's a simple fix? Here's a simple idea:

Hide 4 legendary weapons scattered throughout the map, that way my mid/late-game exploring becomes relevant.

I say 4 because the game was built around 4-player co-op, so every player would have a different legendary weapon with its unique purpose/utility/strength.

Want to add some spice?

Make it a treasure hunt like some runescape clue-scroll where you need to unlock "stuff" at every end of the map that points to one point in the map and you go find the weapon.

Want to add even more spice?

Make it a One-Piece treasure hunt thing with mandatory islands that point to another upon completion, in order to finally find the special weapon/armor.