All those old LucasArts games (Day of the Tentacle, LOOM, Indiana Jones & the Fate of Atlantis, Sam & Max, Grim Fandango, Full Throttle, &c) and similar adventure games (Kyrandia, King's Quest, &c). My mother played all of them and beat them, and while I watched her play I never really managed to finish any of them without looking up guides.