When I first heard about Undertale, I couldn't recommend it. I didn't understand the concept, and I had an even harder time trying to get into it. After much reluctance, however, I can safely say without hesitation or regret that Undertale is perhaps one of the most memorable games I've played.
Undertale is a game that throws conventional RPG elements upside down, and tells a story that is truly heartwarming -- depending on the route you choose. Choices matter in Undertale, and every monster you fight or spare will affect the game's outcome. Gameplay is a mix between a timing-based combat RPG, a dating simulator, and bullet hell nonsense. While none of this makes sense at first, it's something that somehow works when you actually play the game.
Don't take my word for it though. Check it out for yourself.
Everything filling you with determination is bound to eventually fill you with determination... and a lot of save reloads if you're determined to save everyone. Now that's determination!