Zombie is a highly loopable pop/hip-hop song with a really catchy melody, vibrant chord progression, and crispy drums.
Chords: This chord progression is so so catchy, it really feels like it just goes in a circle. The progression is really simple, but different instruments carry the chords in different sections, which gives them a fresh feeling and energy at each point of the song. At the end of the day, the quality of the chords and melody are what people will remember when the hum the song after listening. Note to self: Invest way more time into your chord progressions!
Song Structure: They start the song with an abbreviated hook which helps inform you of what's coming later, and literally "hooks" you. Introducing your chorus as early as possible is almost always a good idea!
Novelty: They do an amazing job of adding new sounds and instruments into each section to bring the beat to life, but the musical ideas themselves (chords and melodies) stay very similar the entire song.
Ear Candy: There are several samples in the background, transition sweeps between sections, lots of stereo delays on the lead vocals, and little things like wind chimes and triangles keep your ears engaged the whole time. These little textures can go a really long way.