I am very up on this album for the following reasons:
1) Production values. This is a beautifully arranged album featuring crackerjack session people. Aside from the vocals, the other Beach Boys barely play on this. Brian envisioned this as a thematic whole and the studio musicians were selected as such to enhance the sound. How many records do you own that so effortlessly weave together sleighbells, light trumpets, tympani and other effects? I am sure this sophisticated layering is what struck the Beatle's fancy.
2) Great song writing. It was Brian's attempt to make a more mature album, with more adult themed lyrics. The songs are haunting in their self-consciousness. Working with Peter Asher, the songs are wonderful compositions that reflect both suburban fulfillment and darker, more troubling visions of post-adolescence.
42 years on, this still feels like a classic. I think musicians will be singing its praise in another 60 years.