It's quite possible that there's no more common interactive leisure activity than singing along to music. It's been a big part of my life for a long time and something that I really enjoy doing and yet is something that, despite the interactivity, I've never looked at from a game design angle. So, I'm going to do that now.
The first thing I want to look at is an underappreciated factor. It can be quite difficult to sing along with some songs. I spent a lot of my youth trying to rap along with Eminem and it was not easy. A couple of years ago, "XO Tour Llif3" came out and I just could not get that pause in the chorus right. The timing just got me every time. It's like a platformer sequence and like a platformer sequence, it felt great when I got it down and also like a platformer sequence, I do it without thinking now. This is textbook video game mastery, but the form is very different.
The Puzzle Game of Half-Remembered Lyrics
Of course, when singing along with a song, we tend to do it imperfectly. Singing ability aside, it's often hard to recall exactly how a song goes, or even to figure out the exact lyrics in the first place. It's almost a puzzle game in that between the structure and meaning of the song and the rhyme scheme, you can often predict much of what you cannot exactly remember and actually having the song play does a lot to jog your memory. The result is like a series of puzzle challenges and it can be deeply satisfying to sing a full verse in the same way.
Similarly, singing along with a lyrics page in front of you can be like walking through a logic puzzle with the solution open. It's very satisfying just to go through something and see all of the pieces click together and understand why things are the way they are.
In all of this, a large part of the experience is in how low stakes it is. I can mess up the lyrics as much as I want and the only person who will know is me and it will only affect me as much as I care. The song keeps playing and I can keep singing no matter how I do. I don't even need to be able to sing well to enjoy it.
I can even modify the difficulty by skipping a verse that's too hard or that I don't remember or choosing to be the backing vocals for a section instead of the lead and it's all fine. It even feels good when you skip a bit or take a beat and then manage to come back in at the exact right time.
You can even self-express with vocalization or ad-libs in the open parts of a song. The rules are elastic and unenforced and that freedom makes for a lot of fun.
Part of the fun of singing along is the lyrics of the song. You feel tough singing "Today I didn't even have to use my AK / I gotta say, it was a good day." in "It Was A Good Day." You feel a very different emotion with "And though I once said I was better off just being dead / better off just being dead" from "No Below" by Speedy Ortiz. A lot of the power of Logic's "1-800-273-8255" comes from singing along with the changing chorus. "I just wanna die today" feels different when it comes out of your mouth.
This is fundamentally different from simple storytelling in a song, and often almost unrelated. Bob Dylan's "Hurricane" is a powerful story told very well, but it's a very different experience than the earlier examples. "Hurricane" is a very specific story about a specific person. There's no chorus. There's no hook for the listener to latch on to so that they can sing themselves. The pace and the music are forbidding. It's an amazing song, but not because of how it feels to sing along with it.
The power of singing along to the lyrics is enabled by how fun it is to sing along with a song in the first place. It's an inherently enjoyable activity. Even where the lyrics are meaningless and trivial, it's just fun to be a part of the music.
B-Side: John Coltrane's "My Favorite Things"
Since I'm talking about interactivity in music, I thought that I might as well put in an addendum about my favorite song, John Coltrane's "My Favorite Things." About 45 seconds into the track, Coltrane plays the famous refrain from the original from The Sound of Music, but then one minute in, he dives off from there into someplace entirely unexpected and yet a place that fits exactly into what came before. Part of the beauty of this is that it understands what the listener anticipates and intentionally does something else. Of course, playing with the audience's expectations is not unusual, either in music, or across the arts as a whole. However, when we look at interaction, we're used to looking at interaction made concrete through rules and numbers, but there's a lot of more implicit interaction that's just as worth considering.