Pretty good show overall. They were smart to construct multiple character plotlines for the entire series; it allowed them to tackle some of their themes and story arcs with a deft hand and just the right amount of pacing.
Johnny and Daniel have the largest character arcs, and the film figures out just the right amount of flaws and virtues to get you invested in both. Johnny's got the more classic tragic hero story, trying to rise above his past demons and to learn and grow, but blindsided by the flaws he was unaware of... Until it's too late and he's left to view the ugly side of his triumphs in his students. Daniel, meanwhile, is still overall a virtuous and forthright man, but he starts the show unbalanced enough to make some serious mistakes and eventually realizes he must reconnect with Miyagi's teachings before he goes off course.
The kids are a tangle of stories. Miguel starts off as pretty much a classic "Karate Kid" antagonist, and the first half of the show follows that outline pretty faithfully... And then the last half forces the audience and Johnny to see the flaws in Cobra Kai philosophy that make this kid repeat history that Johnny realizes should not be repeated. Sam LaRusso is a good character, with her biggest advantage is that they do manage to push her past the "love interest" archetype via her friendship with the frankly awesome Aisha, though they probably can do more interesting stuff next season. Aisha and Eli are both fairly well developed characters, and a very accurate presentation of the benefits of martial arts in assertiveness and defense... And for how bullying cycles around more often then not, with Cobra Kai eventually molding them into classic physical bullies to contrast with the modern cyberbullying and point out how both styles are ultimately messed up petty misanthropy if you don't control yourself.
And the humor of the series is great! From Daniel as the embarrassing dad to Johny as the man so old school that his response to a former All-Valley Tournament champion hogging the mic to talk about peace and harmony is "Kick this sissy ***** in the face," they know how to play with their themes in a humorous style.
Probably the least interesting aspect of the show is Robby, though only because he's written as less of a character and more of an irony-leaden plot device. The actor does a good job, but you can tell they rushed through his "Karate kid" arc because they knew we'd already seen it with Miguel. He's also got more potential for next season.
And I really like how slowly they reintroduced Kreese almost as a theme before actually having him return. Johnny's clearly complicated feelings towards the man are a fairly dark undercurrent when they periodically re-emerge, and the way Johnny Reacts to realizing he's becoming the same kind of teacher in spite of himself is actually kind of heartbreaking. And it says something about the nature of the show and Johnny's arc that, while Daniel is moving towards rebuilding and continuing Miyagi's legacy for the better, Johnny has almost accidentally conjured Kreese up in the flesh from the nether when you know he'd rather excorcise that particular demon.