I mean, part of it is that I am a sucker for these close harmonies between John and Paul. And though they largely move through the verses in simple thirds, the thirds go somewhere a little bit surprising. For me, anyway (because on this song I tend to hear the vocals first) they lead you right into the heart of this song, which is all about the way that the major and minor modes of A talk to each other. Listen to the first verse, for instance. The guitar intro establishes a major key all-too-briefly before the vocals come in on a minor chord on "you know." But as they sing the end of the phrase-- "but I'll be back again"-- you can hear Paul hitting that surprising Picardy third on "-gain." That's just a needlessly fancy way of saying that Paul hits a note that suddenly brightens the whole thing back into a major chord. Of course, then they start up the phrase again in minor, and it happens all over again.
This constant shifting between major and minor is what makes "I'll Be Back" so damned interesting and so lovely-- the song is shifting beneath our feet in rather the same way that the relationship we hear about in the lyrics does beneath John's feet. Nothing seems particularly certain. Isn't this a weird and cool song with which to end A Hard Day's Night? Yes. Seriously, what an odd choice: this was the Beatles' third album, and on the prior two, they'd gone out with balls-to-the-wall rockers, both of which were covers. But on A Hard Day's Night, which was already loaded with such powerful rock songs, it was John's "I'll Be Back"-- which ends the album in this intriguingly ambiguous way, almost with a question mark. The song's significance is compounded by its placement, and ultimately hints at some greater maturity than we've not heard before this point.
I've read that John wrote this just by playing around with the chords to Del Shannon's "Runaway," which is a song that I like quite a lot. I've never been able to hear the similarity exactly, though, so I presume that he messed with it enough to make it something wholly new. But as for the emotional content of the lyrics, I don't seem to remember John ever claiming them to mean much. (Someone correct me if I'm wrong.) We can probably safely file this one away as a very early example of John's self-consciousness and insecurities coming through in a song, as they would later in the much more famous examples from Beatles for Sale and so on. I think you can hear it on John's vocal, too. His vocals when he sings the two bridges solo (sans Paul) are pretty amazing-- they have a certain swagger that shows him, perhaps, a little uncomfortable with this level of intimacy, but you can hear his frustration with himself and with the girl he's singing to as well, and it's fairly intense.
My favorite bit ever is when he sings "I want to go" on the repeat of the first bridge. The first time he sang this, on the words, "I love you so," he did a little melisma thing to make it "so-oh-oh," and throughout the song he's been doing the scooping into pitches that's so typical of pop singing that we barely even notice it. So there's something so naked about the way he sings "I want to go" in this clean, bare, choirboy kind of way. It's almost chilling. It's kind of amazing-- a small detail that makes me squirm. Ditto the long held "I" on the second bridge-- on "I---- thought that you would realize." Again, it's that bare held pitch that does something to me. It's as though the song becomes dryer in these moments, or something, if that makes any sense.
As an interesting exercise, listen to "I'll Be Back" and "Things We Said Today" side by side. The latter was written by Paul, and it sits just a few songs ahead of "I'll Be Back" on A Hard Day's Night. Both of them exploit fluctuations between major and minor modes, and both of them are dominated by a fairly percussive acoustic guitar backing. And both songs are arguably some of the most mature songs that either of the boys had written thus far. I do sort of wonder if one of the songs came first, and then the other came as a competitive response, as seems to have frequently happened with John and Paul. But whereas John's lyrics hint at the troubled persona we'll get to know better down the line, as well as John's own ambivalence about relationships and women at this point in his life, Paul's lyrics have a certainty and an optimism-- colored by a really appealing wistfulness, of course-- that also seem to point to directions to come. I don't know. It's kind of interesting, is all.
Anyway, I'm wicked late today, I know, but we'll have regularly scheduled Beatles going forward. I am totally back.
"I'll Be Back," released in the U.K. side B track 7 of A Hard Day's Night, July 10, 1964; in the U.S. side B track 2 of Beatles '65, December 15, 1964.