The guitar is what pulls you in, the clean electric that lines up with the drums, and it starts off like that Marcy Playground song, just all melody and hook. The voice of Tiger Darrow over the 2nd verse is both unexpected and transformative; the duet that builds up after that is vital, and carries the song.
So what is left, when the pop smoke clears and you can look around the room? The guitar keeps you listening, the pre-chorus is a sweet break and then the chorus delivers a massive lift. This is textbook songwriting chemistry: the lovers' unrest, the two lead vocals, and the production elements coming together to create a simple truth.