Totally fair! They did a good job of making the main storyline playable as a solo player, but the core gameplay loop is still unmistakably MMO-style and not to everyone’s taste.
I love that song in particular because (very minor spoiler) it works both as background music and as diegetic music. In the story, that boss is trying to entice you into going permanently to sleep and living in a dream world where you’ll achieve all your goals and desires, while becoming her meat puppet in the real world. When you’re playing the game rather than watching it with onscreen lyrics on YouTube, you are only sort of half-listening to the song while you focus on the battle, so you don’t realize right away that the battle music is the boss singing to you to seduce you into her flock even while you’re fighting her.
I was impressed by an earlier mod along similar lines, Portal Stories: Mel. Hope this one is as well-done.