There is a reason I love 80s slow jams & rock music, and it's the synthesizer, the echoing sound you get from an electric guitar, and strong vocals, which you definitely get with 50s/60s songs.
The synthesizer is amazing -- it's not just that popping, high-pitch "alien noise". It's also that sorta earthy sound you get when you hit the low keys, the soft melodic sound when you hit the medium keys.
It's also nicely combined with guitars -- often electric and base.
Diving into the guitars, the echoing sound of electric guitars really hit me. One of the best reasons I will go back and back to "Stairway to Heaven" and nearly cry. That's some serious finger work (no pun intended
)
And the vocals -- I need vocals where I can feel the passion in them. High notes, prolonging the notes just a little bit, a bit of a crack in the voice, and the talking you get when someone is encouraging the other background singers to step it up.
Here's just some awesome examples!
Edit: Sorry, I'm really not done XD I nearly forgot the "Wah-Wah pedal" and the amazing violins you hear in old 70s slow jams and 70s psychedelic rock (when they'd have some good orchestras playing for those songs, lemme tell you). They still got them vocals, but man -- I gotta give a mention to that.
Here are MORE examples XD
Here's also more info on the "wah-wah pedal":