AllMusic's Donald A. Guarisco considered "Mr. Blue Sky" a "miniature pop symphony" and a "multi-layered pop treat that was a pure
Beatles pastiche", saying that "the music divides its time between verses that repeat the same two notes to hypnotic effect a la '
I Am the Walrus' and an effervescent, constantly-ascending chorus". Guarisco also pointed out other references to the Beatles, such as "the staccato bassline [recalling] the chorus of '
Hello Goodbye' and pounding piano lines and panting background vocals [recalling] the midsection of '
A Day in the Life. Music critic Nick DeRiso identified several references to Beatles' songs, including "Hello, Goodbye", "
I Am the Walrus", "
Maxwell's Silver Hammer" and "
A Day in the Life".
Billboard described the beat as "catchy" and said that the song builds from a "thumping intro" to a "harmonic operatic" ending.
Cash Box said that the song "features a characteristically full sound and effective use of breaks" and that "fast pace, airy singing and strings provide musical dramatics."
Record World said that "this up-tempo tune guarantees Lynne's legend as both writer and producer and shows off ELO's unique sound."
Ultimate Classic Rock critic Michael Gallucci rated it ELO's best song.
Classic Rock History critic Brian Kachejian rated it as ELO's 2nd best song, highlighting the "bouncing piano groove at the beginning of the song that is one of the coolest rock and pop licks you have ever heard."
Stereogum contributor Ryan Reed also rated it as ELO's 2nd best song, saying that although it was released on the album as part of "Concerto for a Rainy Day", it actually "functions best as a stand-alone art-pop epic, a sort of engorged '
Penny Lane' – built on stomping pianos, manic cowbell...and an octave-spanning choral vocal arrangement." In 2022, Lynne listed it as one of his nine favorite ELO songs. == Personnel ==