It does the best thing a movie to show can do and meaningfully expands the characters and world of the original
It allows Eugene and Rapunzel to grow, individually and as a romantic couple, setting it before they get married instead of just leaving it at happily ever after. The concept of happily ever after itself is kinda central to the show
They bring in new characters that have purpose and dynamics with the originals.
Good long running plot that can still sometimes be addressed in some of the more standalone episodes
Music, art style and animation, you can really feel the effort that was put into it. The show has had a cohesive production and vision behind it and these days that should be more appreciated than ever