An unconventional superhero movie requires an unconventional soundtrack. While Dutch composer Junkie XL (Mad Max: Fury Road, Man of Steel) handles the score, it's the film's use of pop tunes that really strikes a chord with viewers.
No pun intended.
The film's opening credits, which are displayed over a gnarly, hyper-violent fight, are set to "Angel of the Morning" by Juice Newton, a super-earnest slice of early '80s cheese. Tonally, it doesn't fit with what we're seeing on screen, as blood and bullets fly. As a result, it accentuates the splatterfest taking place. It also fits with Deadpool's sense of humor, which is both nostalgic and heavy on the irony.
Neil Sedaka's "Calendar Girl" serves a similar purpose later in the film. The song is more wholesome than a glass of Vitamin D milk, and its lyrics wink at the rapid passage of time we see on screen during Wade and Vanessa's sex-through-the-holidays montage—a montage that is decidedly unwholesome. Other songs, like Salt-N-Pepa's "Shoop" and DMX's "X Gon Give It to Ya" simply illustrate Deadpool's affection for ironic throwback jamz.
The smoothest jam of them all, though, is Wham's "Careless Whisper," which is used as an endearing callback. In the film's first act, Wade tells Vanessa he'll blast it at her in the afterlife, Lloyd Dobler-style, once the cancer's finished with him. Vanessa doesn't want to hear it: not the song, and certainly not the talk of dying. She shuts him down.
When the two are reunited at the end of the movie, Deadpool whips out his phone and fires up George Michael's buttery vocal. It's a playful reminder of the love they shared pre-Weapon X, and a saxophone-saturated suggestion that they've got a lot of life to live together after all.