Why is this song not happy?

There in the Night - El Dorados

To me, it’s a gorgeous piece. But part of that is that it’s a song celebrating a lifetime of untroubled love that somehow has a sad feel to it, giving its otherwise trite sentiments a certain gravitās. I don’t know why, though. From my one class in music, I recall that songs in minor keys sound sadder than ones in major keys. But I can’t tell by ear whether this is in a minor key. If not, what else explains the effect produced?

It’s in a major key. It doesn’t sound particularly sad or anything to me, just reflective/sentimental.

I don’t know the answer to your question but that is one of the great doowop songs ever.

Could be the badly out of tune guitar occasionally soloing riffs over the voices.

Well, for one thing, it’s rather slow, and borrows heavily from the minor key. While slow can sound happy in some contexts, it’s hard to do with the dark vocals of doo wop.

Do you mean that this instance has dark vocals, or is ‘dark’ a term of the musical arts to which I’m unhip?

Slow, and a descending melody line make it sound rather funeral.