Sometimes, in a miscalculated bid to appeal to the masses, actors employ a stereotypical vocabulary of facial expressions and body language. The ensuing delivery is as expressive as mass-produced apartment blocks. By contrast, "Ирония Судьбы" has character innovations that have been edifying generations. British theatre is similarly innovative, and so was American cinema in its Golden Age, except it capitalised on franchises (such as Cary Grant, Jimmy Stewart, Humphrey Bogart, and Fred Astaire), which Soviet cinema rarely did, treating each actor as a character actor.
"Ирония Судьбы" is not a comedy. It has a genre to the extent that a life (when crafted carefully) does. In life, comic situations do not befall stand-up comedians. They befall those who seek novelty, which conflates genres.
The picture is about seizing the moment, about friendship, about the supremacy of love, and about the clarity of vision. It is easy to overlook a potential infatuation, but not potential love, which promptly casts the couple in a play written just for them. The right lines spring up naturally (and are perceived as right also naturally).