1) How much in control Brian Wilson is of the entire production. He was the writer, arranger and producer of the song so he knows exactly what he wants and he's very direct in getting it from his players, who were the cream of the crop of Hollywood studio musicians.
2) The song was done on a 4 track tape recorder at the now defunct Gold Star studios in Hollywood. That means that the entire band had to play at once in the relatively small studio area. Gold Star was originally a small demo studio that came to prominence thanks to Phil Spector and his many hits. It's still the same today - when a studio is hot, everyone wants to use it (same with the musicians).
3) Like many other Brian Wilson productions, there are 3 basses on the song. The genius is that they all rarely play at the same time, with the Fender bass played in the verses and the upright during the B sections and bridge. The 6 string bass is actually a baritone guitar that used to double some of the lines.
4) Hang in there until 6:10 when we get to hear the famous Beach Boy vocal harmony overdubs as they were being recorded at Capitol Records studios. These guys were so good!!
5) Notice the small tuning inconsistencies in the guitars and horns. This doesn't seem to bother Brian at all but it would never fly today, nor would some of the small timing errors.
6) Also notice the loud click every time that Brian hits the talkback switch. This was a problem on a lot of early consoles that used to annoy the heck out of anyone out in the studio or wearing phones. It was cause by chattering analog relay switches that weren't tamed until a digital alternative came on the market in the 80's.
Considering that this was just some audio out-takes, the video that goes along with it is extremely well done and keeps your interest through the entire piece. It's an awesome piece of musical history that really shows how a hit was made way back when.
Don't forget to check out my Music 3.0 blog for tips and tricks on navigating the music business.