Pokémon Mystery Dungeon: Red Rescue Team was the game always found in my GBA and later in the DS bottom slot. I must have completed this dungeon crawler a dozen times and I enjoyed every single playthrough.
As dungeon crawlers go, Mystery Dungeon is rather basic and not overly challenging. However, for the intended age range and as an entry in the Pokémon franchise, Red Rescue Team holds up remarkably well.
The music is strong, the dungeons all have a unique aesthetic, and the main storyline is good: nothing exceptional, but deeper than most Pokémon games.