Borderlands 1
It's the perfect game. The story is tight. The builds and weapons are fun. It's not too grindy, but you can benefit from grinding if you want to. The post-apocalyptic trash planet setting has yet to be diluted and the characters have yet to be flanderized by later entries in the series.
It's a game that I can pick up anytime and just vibe. My favorite part is collecting all of Tannis' ECHO Logs throughout the game and getting to follow along with her trauma and descent into madness.
It helps that it has the second best DLC in the series to date. Secret Armoury of General Knox is chef's kiss. Assault on Dragon Keep is only better by a hair.