This one is a bit subjective but I'm curious as to what campaigns you've run that you are your players thought rocked the hardest ?
My list, not in order
#1 Thieves Night Out . AD&D 2nd edition.
All players are thieves or thief multi-classes with humans aloud to multi-class with thief for this game. Basically it was a caper game kind of Guy Ritchie, before Guy Ritchie meets D&D. There were 3 regular players plus up to 12 (far too many BTW) at one point and simply it worked. The players had motivation, verve and at one point were so immersed in the roleplaying one broke out in sweat.
#2 Midrea Unglued. AD&D 2nd edition.
The party was two barbarians Hans and Franz cribbed from Saturday Night Live , Rambo the awakened squirrel , Hayabusa the mute coroner, Inga, Hans and Franz's minder and a Satyr whose name I long forgot. It was played semi-straight but for laughs and given the inherent zaniness of D&D it was incredibly fun.
#3 Santa Carla Chronicles. Buffy RPG
This is three games actually . Buffy meets Blade meets Lost Boys with a tiny smidgen of Great Teacher Onizuka , Duke Nukem and Elvira . This ran into 2 spin off campaigns, one with the characters on the run in Colorado and another 60 years into the future. All of the games had harrowing moments, Whedonesque humor , great roleplaying and charm. Truly a wonderful gaming memory over a couple of years
The Return of Planescape? - Curious. There is a brief note on this 'countdown' at Enworld.
15 hours ago