Going back to the Beach Boys:
Underneath the beautiful harmonies and fun songs about surfing and cars, the Beach Boys' songs seem much more heartfelt and vulnerable than those of their contemporaries, even to the point of coming off almost a little awkward. It feels like there's an emotional barrier of self-consciousness that most of us have that they seem to push right through without even realizing it, which is just refreshing and lovely in itself. There's a pulse of disarming positivity throughout all of their songs, even the weird and weepy ones. They were precious with the musical side of things, but the lyrics felt natural and unpolished, even for that time. The Beatles, on the other hand, always sound kind of detached from their songs like they are doing a recording of their rehearsed performance art, and it's easier for me to actually believe the Beach Boys, but maybe that's just me. Like, at the beginning of "Don't Worry, Baby," when he says in the opening line: "well, it's been building up inside of me, for, oh, I don't know how long..." it just feels way more true than any Beatles song I can think of, and the song only just barely started, haha. It's also hard for me to think of another band who wouldn't think they're too cool to record a probing, intimate song like "In My Room" - it's just so on the nose and leaves you nothing to hide behind, but somehow they pull it off and you don't pity them or feel uncomfortable about it because they're not really complaining at all, just opening a door and letting you in on who they are.
Also, the good-natured exuberance in songs like "Heroes and Villains," "Sloop John B," and "I Get Around" just gives me a certain thrill that no other band has ever matched, and I think part of what makes those songs really take off is the feeling that the artists performing them are grounded in a level of authenticity and they're really as excited as they sound.