>>718708142
It's actually a really good game, but the "game" aspect of it is lacking compared to other RPGs. (It's a bit lacking for a bullet hell too, but there are some really high points.) People usually play it for literally everything else about it, ie the story, the characters, the music, the cool pixel art, etc.
Though its good in its own right, you'll have to play Undertale first to truly get the hype. It's not a "sequel", but a "parallel story". Not my words, just the dev's. He's really cryptic about it.