I loved Himawari-san.
It's not your typical GL. In fact, very little happens on the surface when it comes to GL. The story is told through slight movements, subtle hints, metaphors, flashbacks, and meaningful stares. It's like everybody understands everything, but they never say it.
You have probably heard that, in Japan, the phrase meaning "The moon is beautiful tonight" is a subtle way of confessing your love. Well, this double-layered, simply phrased, and profoundly meaningful narrative is what you should expect from this wonderful manga. It is absolutely brilliant. Poignantly beautiful. With its aching exuberance of veiled innuendos and barely concealed vulnerability, this whole story is a masterpiece where you get almost no action. It's not a CGDCT; it barely counts as a slice of life, although it bears traces of both. Moreover, arguably as a reward for being so invested, you even get the actual phrase about the moon at a certain point.
In the end, it is a very poetic and deliberately understated love story in which you hardly see any literal, obvious love. It is very gentle, kind, and slightly sad. There is an abundance of love under the surface, though. It is truly beautiful. But it's like a haiku stretched across 13 volumes. Minimalistic and painfully profound. Unless you are ready to read this mass of meanings between the lines, it would hardly impress you. Of course, it's alright if you aren't. I write this just to let you know what to expect from this manga, after all.
I can't recommend it enough. But, I understand it, not everyone is after things like that. If you're looking for a more "traditional" yuri with emotional struggle and self-doubt, this isn't what you're looking for. But if you are looking for an extended ode to love that retains the minimalistic essence of concise Japanese poetry, that's your best shot.