I like a lot of songs s-l-o-w-e-d down.
I heard the Battle Hymn of the Republic slowed down to a somber, even lugubrious funeral dirge at a funeral a few decades ago, and I still remember how it brought goosebumps to my skin and chills down my spine, like it was digging into the depths of my soul. WAY, WAY better than the usual "rousing" renditions that do nothing for me. It re-defined the song for me, permanently, making most renditions hopelessly "wrong" to my ears.
The slow version of Micheal Jackson's "Billie Jean" as covered by David what's-his-name on American Idol, I think is MUCH better than the original, as is Foy Vance's largely slowed, plaintive version (before he speeds it up towards the end).
A lot of other songs become more expressive, emotional and soul-stirring when slowed down, but they also usually become more challenging to sing well, as the subtler nuances have to be brought out and controlled. Done poorly, they can be boring or just plain bad. But in the hands (well, throats) of good singers, slowed-down songs can be great!
Of course, some songs improve when speeded up. I have an almost certainly bootleg/counterfeit cassette tape of a dance hit from some years back ("Ride on Time" by Black Box) that I picked up in Thailand. I didn't overly care for the original, but this one was recorded around 7 or 8 percent faster than the original (but without pitch change, if I recall correctly; haven't listened to it for a while). It's great! The whole feel and "energy" of the song is transformed by the speed increase, even though I think the shift was unintentional, possibly because of a difference in 50 vs 60 hz gear. --or maybe intentional, to save the cost of a few feet of tape?
I have a Denon CD player with a speed adjustment that allows changing speed while keeping pitch, up to +/- several percent. Sometimes on a whim, I'll experiment with slowing down or speeding up songs. Most of the time it does not improve them, but sometimes it definitely does. Just depends on the song.