"I don't regret walking with you through wind and snow, or emptying those cups together.
On the stage, our souls face each other, and I'm a little bit ashamed.
Because even if I don't say anything, you always understand everything."
(–My translation of some lyrics from the ending theme)

TL;DR: if you're put off by the "Beijing Opera" theme of this drama, that may look old-fashioned and boring at first (it was for me), don't be. Watch it. You'll end up wanting to learn more about Beijing Opera and falling in love with the characters and their relationships. And crying too.

Winter Begonia is, in my opinion, the best long-format Chinese drama of 2020. This series does something that was never attempted before in any drama, and it does it beautifully: it takes us behind the scenes of the Opera world of Republican-era Beijing and lets us look closely at every exquisite detail that made up that world, from the precious costumes, to the colorful makeup powders, down to the clinking of the porcelains and the fuming cups of tea. And it takes us into the lives of people who lived in that world letting us taste their joys and their sorrows, always in such a vivid and evocative way that I've rarely seen in other dramas.

This drama has no filler scenes, no overused tropes; every character and every detail has a purpose and is treated with love and care. This level of care also applies to the technical aspects such as photography, editing, color grading and music. The music is especially beautiful, and the opera melodies are perfectly blended into the score. The costumes and makeup are gorgeous, and the Dan (female role) costumes and makeup look sooooo good on Yin Zheng. He's like a doll. And watching this drama is like looking at a series of paintings.

Shang Xi Rui, played by Yin Zheng, is undoubtedly the star of this drama. A genius performer who's only known a life on the stage, he's stubborn, hot-headed and has got the heart of a child– qualities that cause him to be unfit for a society made of rules and courtesies. When we meet him and for most of the story, he's like a cute puppy that turns feral when he's angry. But he also grows a lot and has great character progression, which is beautiful to watch.
At one point, Cheng Feng Tai says of him, "The other performers look like the characters they play. Mr. Shang IS the characters themselves." I think this quote also applies to Yin Zheng in his phenomenal portrayal of Shang Xi Rui. After watching him you won't easily forget the way Rui-ge runs, eats, laughs, cries, pouts or smiles. Or the way he speaks, with that unique, cute way of speaking and soft Beijing accent. It's a fantastic performance that will live on for the ages. A comparison with Leslie Cheung's Die Yi from "Farewell My Concubine" can't be avoided because of the similar roles, and Yin Zheng passes with full marks in my opinion. He's honestly just as good.

Dashing businessman Cheng Feng Tai (Huang Xiao Ming) is Shang Xi Rui's "god of wealth", patron, pillar of strength and his perfect counterpart. Where Xi Rui has his head in the clouds, Feng Tai has his feet on the ground; where XR is the reckless and pure-hearted child who always wears his heart on his sleeve, FT is the one who knows better how to navigate the nastiness of the world and keeps all the pain inside him. They also come from opposite social backgrounds as XR is basically illiterate and belongs to a profession that is treated as pariah, while FT is the richest guy in town who's studied abroad.
Cheng Feng Tai is not a really complicated role to play, but it would have been easy to slip and make this character too dull or too cheesy, or without chemistry with SXR. Huang Xiao Ming instead plays him as a well rounded character that balances the worldly, dashing hero part of FT with the conflicted, often flawed one. And the chemistry is there. He IS Shang Xi Rui's own beloved Er Ye.

The ensemble cast is excellent, and all the subplots and the background elements stand on their own and are never just filler in between the main leads' story, or wallpaper. But the dynamic between the two leads is of course the highlight of Winter Begonia.
知音 zhiyin is the word used to describe what they are to each other: closest friend, confidant, soulmate. Someone who can understand the other with no need for words. When others doubt Feng Tai's alliances, including FT's own wife, Xi Rui trusts him completely; when XR is hungry or hurt, FT is there to feed him or take care of him; when XR is lonely, the only thing he wants is having FT next to him. They're fully devoted to each other and would die for each other (this is not an exaggeration, it's what they really try to do). One of my favorite lines by Feng Tai to Xi Rui is "You think I won't be there to care about you [when everyone else abandons you]? Only when I'm dead!"
For them, the unspoken is heavier than the spoken. They never outright say what they feel about each other (of course, due to drama censorship too) but they still say it with their actions and expressions. XR says it singing on the stage, FT says it with THOSE LOOKS when he's looking at XR sing.

Finally, I won't say this drama has no flaws (that's why I couldn't give the story a 10/10). I think it has flaws in the stereotypical portrayal of most of the Japanese characters, in how some secondary characters could have been written better, in the not-very-clear passing of the time (it's always winter, the babies are always infants, the women are always pregnant). The execution of the story is also not flawless in terms of how the story beats connect to each other. But honestly, these things don't really matter when you look at the bigger picture. Which is an incredibly beautiful one.