There are so many things I loved about this film I'm not quite sure where to start, but I'll try to cover some of them. If/when you finish reading my ramblings, go and read this coherent and informative essay about the film by Jonathan Rosenbaum: https://www.criterion.com/current/posts/4543-good-morning-structures-and-strictures-in-suburbia
Firstly, I'll just say that I initially found this a bit difficult to get into - a lot of characters are introduced quite quickly and I wasn't fully concentrating, so I lost the thread of who was who and how they were all connected. I restarted the film after 20 minutes, engaged my brain properly and from thereon I really enjoyed it.
I loved the intimacy and intricacy of the space that the film takes place in - the 'action' mostly takes place in a series of detached but very closely connected houses. Characters routinely pop in and out of each others' houses, call to one another through doors or windows, and scurry up and down the narrow pathways between them. I've never really taken the time to analyse why, but I am always drawn to films that take place in spaces like this - discrete but connected, blending private and communal (I love the Dekalog films for this reason, and also pretty much anything set on a train).
Then of course there are the characters that inhabit these spaces. They are an eclectic bunch spanning the generations, from seven year old Isamu (a delightful performance from Masahiko Shimazu which I promise will make you smile) all the way through to an imposing grandmother who turns the tables on a pushy salesman with a 'Crocodile Dundee' style move of producing a knife much larger than the one he routinely uses to intimidate his unwilling customers with. There are gossipy housewives, bohemians with western film posters on their walls, unemployed drunkards, shy twentysomethings tiptoeing around their feelings for one another.... All have their flaws and foibles, but I don't think there is a single character in the film depicted without empathy.
Empathy is the word I keep coming back to when I think of Ozu's films. In reading about this film, I came across the Japanese concept of 'Mono no aware' which is worth looking up if you're not familiar with it. Variously translated as 'the pathos of things', 'an empathy towards things' and 'a sensitivity to ephemera' (thanks, Wikipedia), it captures the warm, wistful, bittersweet nature of Ozu's films.
It is also very funny. All the Ozu films I have seen contain subtle, gently comic moments - this one however is more of an out and out comedy. Fart gags abound, and the film opens with one of the schoolboys 'sharting' - 45 years before Philips Seymour Hoffman had to explain the term to Ben Stiller in 'Along Came Polly'.
Throughout the film various contrasts are shown between the childrens' world and the adults' world - most specifically in the way that the children are direct in saying how they feel and what they want, whilst the adults speech is diluted by social niceties and empty language (including the phrase 'Ohayo/Good Morning', giving the film its title). The indirectness of the adults' speech hinders a young couple from expressing their true feelings for another, as well as to various comic misunderstandings amongst the gossiping housewives. But Ozu is not being cruel to the adult characters in his film - he is not cruelly mocking them for the absurdities of these 'social lubrications'. He gently teases them, for sure, but always with empathy and an understanding of the necessity of such modes of speech.
I'm sure there is more I could say - this is such a rich film - but I have surely already written more than any sane person who has stumbled across this review is likely to read, so I'll finish there.