I remember exploring every variation and solution to Maniac Mansion (NES microwavable hamster version).

Xenogears for PS1 is still charming. Chrono Cross maintains great replay variation and is interesting to see a proto version of the D&D 5E spell slot system.

Douglas Adams fans should certainly try out Starship Titanic at least once for the NPC chat aspect. It was "mess with Siri" before Siri was ever around.