TL;DR at the end with no spoilers.

Yeah, I'm a sucker for happy endings, just like you. This one's not happy, but it's arguably one of the best assets of this show. Hear me out.

I think When We Were Young has a rather weak start and markedly improves as the episodes go by. The main reason for that is the ML, of whom in all honesty I wasn't really a fan early on. He's this Gary Stu that can do anything better than anyone: the first time he enters the classroom they have him run his hand through his hair in slow-mo like the world revolves around him, he tops the school rankings for his year, is kind of a science genius, can play basketball, can kick everyone's ass in a fight, can repair his own house, and can even sing and read sheet music—though, to be fair, this last point is revealed much later on. On top of that, he enters the FL's life at full throttle without regard for personal boundaries, as if he had read the script and already knew he'd get the girl in the end. I realize this tries to appeal to a certain audience, but still.

In the same vein, for the first few episodes the show wasn't really able to get me to suspend my disbelief. For instance, in Ep. 2 the ML carries two iron pipes in his backpack; we're later told that he's building a handrail for his grandma at home, but he gratuitously brings those iron pipes to school and the teachers don't ever acknowledge that—you know, normal student behavior. Later in the episode, the FL is jealous of the ML because he was named the new class representative and sets up a fight between him and some random dudes to teach him a lesson; she's lucky that the whole thing is handwaved with comedy, because it could have gone ridiculously wrong. Again, no one ever acknowledges it. The show has some more moments where the gravity of a situation is clumsily written off via comedy, but these two stood out the most for me as my suspension of disbelief was at its lowest. All that might be perfect for a show like Nichijou, but not if you want your story to be taken seriously.

Fortunately, it gets better. By that point I'd rolled my eyes a few times and was ready for another disappointment, but I don't regret seeing it through. As the story progresses, the relationships between the ML and his new friends settle in and develop, and his personal circumstances start to seep through and give nuance to his initial Gary Stu-like characterization: it turns out he's poor and his only relative—his grandma—is visibly declining due to Alzheimer's, and the plot doesn't give him a cheap way out. I'll admit that one of my worst fears is developing any kind of dementia one day, and that I'm biased by that, but I think the struggles he goes through help make the character believable in the end. Also, kudos to him for not turning into a jealous, passive-aggressive bundle of insecurities whenever the FL doesn't look his way, which was driving me nuts in the previous two dramas I watched.

The FL and his childhood friend, who are the other two thirds of the love triangle, also get their fair share of character growth. I don't have any significant issues with them aside from how the improvement of the FL's academic performance (a key point of her character) was shown on screen; I felt the plot couldn't decide whether she was hopeless or not and that made her eventual success seem a little bit ass-pulled. Excluding that, I liked their evolution beyond the initial archetypes of "stupid but athletic girl" and "unexpressive boy who bottles it all up".

The way the remaining two main characters (it's a group of five friends) are fleshed out is not at the same level, though. The new-rich kid uses his dad's money to help his friends and is kind of a comedic relief, but the show also wants us to take his family hardships seriously while at the same time refusing to elaborate; he feels neglected by his parents but, apart from a couple arguments with his father, a random scene where his mother briefly comes back from overseas when he gets injured at school, and another one where his mother leaves them for good, we don't get much insight on how it all came to be that way in the first place. There are also a few scenes with him and the head teacher that hint at potentially some kind of positive dynamic between them, but that path was discarded too. All in all, he feels like a Doraemon of sorts whose job is to produce unlikely plot devices to serve other characters' own development. As for the girl with overbearing parents, I really thought she would get a nice arc where she made her parents see her as an independent person, maybe by doing things her own way and succeeding, but that's far from what happens. She eventually locks herself in her room for days and then proceeds to fail the university entrance exam, after which her helicopter mother does an absolute 180° and comforts her at the gates and takes off again mere minutes later. And, just like that, her lifelong family problems are officially fixed. I mean, failing the exam due to not studying enough is a fair outcome—even if she was under unreasonable pressure—but the attitude change of her mother comes out of fucking nowhere. For the most part these two characters are fine, though, it's just that for me they lack depth for all the screen time they get.

Anyway, this is getting long, so I'll wrap up with the original point I raised: the ending. By the end, all the main characters must make difficult decisions due to either their own actions or their circumstances. It would've been tempting to force the stars to align for a cheap happy ending, but luckily it didn't go down that path. Now, it's not spectacularly sad nor ground-breaking, but it does a good job of tying together everything the show had been building up emotionally. It doesn't come up with last-minute time skips that throw away an entire season's worth of storytelling, or force incompatible people together because the script said so. Here, the main cast part ways with each other and they know it's the best (or only) option they have, and make peace with things they can't escape. Regardless of whether you like how they got to that point, at least it follows through with the consequences. This alone is more refreshing than I'd like to admit.

TL;DR:

Gary Stu ML transfers into the FL's school and makes friends with the rest of the cast while steamrolling everyone with his talents. As the story progresses, the character gets more nuanced and the show improves as a result, which is relevant if you're less than impressed at the beginning. Three of the five mains have the most focus and development, but I expected more for the other two, which is a bit of a shame. Their interactions are fun and interesting to watch, although some situations they're put in felt a bit unlikely to happen. The ending is bittersweet but coherent in that making it happy would detract from it, and I like that for a change.