Mario Kart DS is the absolute king for me. The amount of hours my friends and I spent on Balloon Fights are incalculable. Somu fun... Shame battle mode hasn't been the same since MK7. MK8D improved a bit... But I don't know, it's still lacking something. The arenas from the DS and Wii games were amazing...
Wii Sports and Wii Fit (and all their iterations) were also fantastic. I played them with my family for years and we had an awesome time with them. Bowling was legendary xD
And... These are not the ones you would first think when talking about offline co-op games... But Mario Galaxy, Subspace Emissary from SSBB and Star Fox Zero were unforgetable co-op experiences for me. In Mario Galaxy the co-op was kind of simplistic, but regardless, meand my sister were so happy to play this game together during 2008's winter... Subspace Emissary was super epic to play with a friend of mine... And Star Fox Zero went from an average game on single player... To one of the best on the Wii U thanks to co-op. One of us would shoot and the other would control the Starwing. What a journey. It was super intense and inmersive. "Move that way, we gotta shoot that son of a bitch!" "Shoot in three, two, one... NOW! ". SO FUCKING GREAT.
