Undertale is an indie RPG with a lot of heart.
Pro Amazing characters
The characters in the game are written well, each with their own personality. One may be too nice, and will lower their hit points when you attack, just to not offend you. Another may have personal goals of validation from their friends and family. This well fleshed out world works thanks to the characters contained within, making for an enjoyable story filled with humor.
Con Replaying can be a chore
The first time going through the game it's a nice experience, especially when we know nothing about the game. A different story is when we try going the same route and try changing one thing. Not only all the jokes and plot points have already been experienced, it can take a while to get to the point when we decide to do something different.