Maybe the Blaster Master games, they always had a sense of exploration to me.
Old-ish exploration platformers
Jayden Hall
Luis Phillips
Nifflas' Within a Deep Forest and Knytt/Knytt Stories are breddy nice as far as exploration games go. Freeware.
Indie stuff before indie stuff was exclusively trash.
I'm not sure about the newer Knytt game. Something about the presentation is just wrong.
Isaiah Wright
Exile
Cauldron 2
Impossible Mission 1, 2
Head Over Heels
Jaxson Bennett
Fuck, that looks good.