UNDERTALE has an amazing storyline, amazing soundtrack and amazing overall gameplay. UNDERTALE has 2 main endings, (Pacifist and Genocide), which both have their own completely unique storylines that still link in with the full story. Without giving away too much, if you're into games which constantly break the 4th wall then this is the game for you. Also, if you somehow get bored after completing both Pacifist and Genocide, how about trying to get all 90 (ish) neutral endings? Or how about hard mode? I could talk all-day about all of the neutral endings and how they change depending on everything between who you killed and how many food items you ate! There's so much to do in UNDERTALE for all ages.
10/10 would recommend.