If you want to ruin your life and sink a couple thousand hours into something, Warframe is free, has a decent backstory and a few bangers on the soundtrack.

The regular gameplay loop boils down to “Be a ninja with space magic, build weapons and biomechanical suits of armour out of blueprints that RNG drop from different enemies to customise powers/damage types, level up weapons to rank up so you can get bigger and better weapons, save the solar system with the power of friendship and this gun I found.”