Undertale is a new 8bit RPG that's much different from the rest. In most games, you have to kill bosses and monsters to survive. In this game, it's up to you whether you want to kill anyone, and depending on your choices, you can make friends that you would have lost, engage in secret fights, and much more. You have so many choices in the game that you can replay it over and over to achieve all the endings. But be careful, because even if you reset the game, some characters might have a vague memory of you.
The fighting style of Undertale is also unique. When an enemy attacks you, instead of automatically losing your health, you can dodge their attack by moving your "soul" across the screen to avoid being hit. Because of this, you don't have to lose any damage throughout the battle.
Undertale starts by your character falling down a giant hole at the top of a mountain and waking up in a world full of monsters. They were all banished to live apart from society for the rest of their lives by humans who sealed them underground with a magic spell. The monsters have figured out that the only way to undo the spell is to have the power of seven souls, but since monsters' souls disappear after they die, they've spent years killing the humans who fall into the underground to gain their souls. Because of this, most of them want to kill you so they can leave, but it's up to you if you want to hurt them back, or show them that you both can find peace.
I highly recommend going to Steam and buying Undertale. I'm 12 and it's my favorite game, while I also know adults who love it as much as I do.