Beat on pacifist for my first playthrough. Gameplay and puzzles are okay-- not all that fun or interesting. I don't really think it's that funny, but I knew that was something about the game that everyone liked. I think everyone likes the story as well, but I can't say it really left that much of an impression on me. Maybe I will play it again in the future and enjoy it more, but for now, I only liked it a little bit mainly for the boss fights and the music.

EDIT: You know what fuck it, I think about Undertale probably once every two weeks at least since finishing it last year. Story's a thinker