While the main story of Dead Island 2 has plenty of content, there are many side quests worth doing to acquire weapons and level up, which will, in turn, only make the game easier. For example, the Clean & Snatch quest is a short side quest that revolves around collecting a couple of clues to unlock a chest that contains a valuable sword.
https://screenrant.com/how-to-beat-clean-snatch-quest-dead-island-2/