It feels like a montage of choruses from different songs focused into one theme, set to the tune "on melancholy hill"

This is a minute and fifteen seconds of edited and selected works that you've formed into a single piece. It's been said that every story has already been told, and as a mashup creator you're able to pick out themes and concepts from this expansive library of music that you're familiar with and turn it into something unique. It's a "New Classic"

Music has an art that can consist of musical expectations, timings and repetitions.

tl;dr

Mono no aware (物の哀れ, もののあはれ), literally "the pathos of things", and also translated as "an empathy toward things", or "a sensitivity to ephemera", is a Japanese term for the awareness of impermanence (無常, mujō), or transience of things, and both a transient gentle sadness (or wistfulness) at their passing as well as a longer, deeper gentle sadness about this state being the reality of life.