Lennon expressed his esteem for the song in his 1980 Playboy interview:

“ LENNON:”All My Loving” is Paul, I regret to say. Ha ha ha.
PLAYBOY: Why?
LENNON: Because it’s a damn good piece of work. … But I play a pretty mean guitar in back.”

The complicated rhythm guitar is probably the reason that John left the deep singing part (in the last verse) to George, he simply couldn’t do both.
Cynthia Lennon believed John wrote it for her, but in fact Paul (the writer) probably had Jane Archer in mind when he wrote the lyrics.

We should also pay attention to Ringo’s great drumming, it has a very distinct and difficult to copy, latin style. It add a sophisticated rhythm to a song that without it would much more ordinary pop/rock, this is evident on the Live at the BBC  album were he plays an ordinary 4/4 rhythm. It gets a more rock’n roll feel but loses a bit of it’s uniqueness, I think.

Wikipedia:

Single by the Beatles
from the album With the Beatles
B-side	“This Boy”
Released	22 November 1963
Recorded	30 July 1963
Genre	Rock, pop
Length	2:04
Label	Parlophone (UK), Capitol (Canada)
Writer(s)	Lennon–McCartney
Producer(s)	George Martin

“All My Loving” is a song by the Beatles, written by Paul McCartney (credited to Lennon–McCartney), from the 1963 album With The Beatles. Though it was not released as a single in the United Kingdom or the United States, it drew considerable radio airplay, prompting EMI to issue it as the title track of an EP. The song was released as a single in Canada, where it became a number one hit. The Canadian single was imported into the US in enough quantities to peak at number 45 on the Billboard Hot 100 in April 1964. It is often considered Paul’s first major work, and rightly so.

It took 13-14 takes to get the song right in the studio 30 July 1963.

The Beatles – All My Loving:

“It was the first song I’d ever written the words first. I never wrote words first, it was always some kind of accompaniment, I’ve hardly ever done it since either.”
– Paul McCartney (Paul McCartney: Many Years From Now – Barry Miles)

Like so many of his [McCartney] happiest moments, the arrangement features a wide-flung walking bass, spiced up by fast rhythm-guitar triplets Stolen by Lennon from The Crystals’ ‘Da Doo Ron Ron’…. one of the best-recorded songs on With The Beatles, benefiting from an open, spontaneous sound and minimal overdubs. Despite some wobbly pitching, McCartney’s vocal is as irresistibly joyous as Harrison’s Carl Perkins-style guitar break and the brightly lolloping beat of the track as a whole.
~Ian MacDonald (Revolution in the Head: The Beatles’ Records and the Sixties)

The Beatles – All My Loving (Ed Sullivan 1st appearance):

“For all of its almost utopian feel-goodism, “All My Loving”‘s melody has a bittersweet quality that keeps the tune from even approaching sappiness, particularly on the chorus, when McCartney’s vocal is complemented by haunting descending harmonies. It was this bittersweet element that separated the Beatles from not only their Merseybeat competitors…

…”All My Loving,” and not “I Want to Hold Your Hand” as some might guess, was the first song that most Americans saw the Beatles perform, as the opening number of their appearance on the Ed Sullivan Show in February 1964. It was not released as a single in America, but in all likelihood could have been a huge hit if it had been.”
– Richie Unterberger (allmusic)

Paul McCartney: vocals and bass
John Lennon: backing vocals and rhythm guitar
George Harrison: backing vocals and lead guitar
Ringo Starr: drums

Lyrics

Close your eyes and I’ll kiss you
Tomorrow I’ll miss you
Remember I’ll always be true

And then while I’m away
I’ll write home every day
And I’ll send all my loving to you

I’ll pretend that I’m kissing
The lips I am missing
And hope that my dreams will come true

And then while I’m away
I’ll write home every day
And I’ll send all my loving to you

All my loving, I will send to you
All my loving, darling I’ll be true

Close your eyes and I’ll kiss you
Tomorrow I’ll miss you
Remember I’ll always be true

And then while I’m away
I’ll write home everyday
And I’ll send all my loving to you

All my loving, I will send to you
All my loving, darling I’ll be true
All my loving, all my loving
Ooh, all my loving, I will send to you

–

Check out:

36. All My Loving (written by Paul McCartney ~100%)
37. I Want To Hold Your Hand (Lennon/McCartney – 50/50%)
38. Taxman (written by George Harrison ~100%)
39. Because (written by John Lennon ~100%)
40. All You Need Is Love (written by John Lennon ~100%)

– Hallgeir & Egil