“Any album (Shut Down, Vol. 2, 1964) that can begin with five minutes of material on par with ‘Fun, Fun, Fun’ and ‘Don’t Worry Baby’ is going to be worth something (JohnMcFerrinMusicReviews) … The second half starts on a pretty high note with the band’s cover of ‘Why Do Fools Fall in Love?’ (which would be a pretty trite choice if the song didn’t fit the band’s vocal talents so well), and ‘Keep an Eye on Summer’ at least sounds like a classic Beach Boys ballad (even if it’s not striking enough to rank as one of the band’s best).
… The best thing that ever happened to the band was for this album to not do especially well on the charts; while it wasn’t exactly a commercial dud, it struggled enough to creep up the charts for the band to realize that they were already on the verge of becoming an anachronism, and it helped make clear that the band needed to change some things.”
“Keep an Eye on Summer” begins in F# major, shifts to Bb major at 1:06, lands back in F# at 1:33, and then powers through an intense a cappella half-step key change up to G for the outro.