This is a very niche answer, but might be the single song I've had the biggest turnaround on. "Sabbath Prayer" from the Fiddler on the Roof soundtrack.

It's set up to be so skippable. It's nestled between two more upbeat songs, "If I Were A Rich Man" and "To Life." It's just a prayer, so it doesn't advance the plot. It's very slow to start, with a long, quiet intro for a stage piece (~30 seconds). Even when the first lines kick in, it's very morose, and the two voices are mostly repeating a single note.

I don't know when I sat down to listen to the whole thing, but it's so worth it. If it comes across as slow, that's of course because it's supposed to be a serious, contemplative moment of prayer, and appropriately, it builds into something rapturous. As more voices are added, the harmonies get more complex, and they start to have different vocal lines weaving amongst each other, all culminating in one of the most epic sung chords I can think of. It's simply beautiful, and I never skip it now.