The thing with Chapter 1 is that it was fantastical. There's a magical forest, whimsical characters, and weird birds.
Chapters 2 and 3 on the other hand are all modern. I doubt that I need to explain why. While still good, these take away from how the game should feel, which is a fantasy with a prophecy and magical characters.
Chapter 4 goes back to a more fantastical setting, which is one of the reasons why it's so good.
Overall, 1 > 4 > Undertale > 2 > 3