Ultimately, Undertale succeeds because it captures the heart of the player and makes the player care about the game.
I’d love to dive deep into the details, but honestly, that would spoil the whole point of Undertale - its surprises, its secrets and its complexity. This allows for multiple playthroughs as players figure out how different types of actions by them create entirely different storylines. Every decision you make triggers different outcomes, which allows players to experiment with the different reactions NPCs (non-player characters) give them.
