Art is nice, and the comedic expressions are very well-done.
Characters are well-developed as well. MC is an OP youngin', but there are valid reasons for his ridiculously strong martial arts. It's not like his skills just popped out with a simple "he's a genius" explanation.
That said, I do have to note his reincarnation really only comes into play regarding his otherwise inexplicable skills. His is kinda childish (through progressively less-so) and his attitude towards his parents in this life is respectful and surprisingly loving. (The family fluff is adorable and heart-warming.)
He does refrain from calling his mother "mommy" in favor of the more formal "mother" (which I suspect was '엄마' and '어머니' in the original), but otherwise, his age/experience does not carry much weight in his interpersonal relationships or general bearing. At least until he starts meeting people from his old life.
His mentality being closer to that of his current physical age is actually a blessing imo, though, because his love interest is around his age. If he behaved as his cumulative mental age, any romance would come off more than a bit pedo-/ephebophilic. So. It's better to think of him as a teen with the skills of a grown man.
His family and even some of the servants (especially Kyungho) have their own personalities, and their interactions with the MC don't feel forced or one-dimensional.
I even liked the female characterization (mainly represented by his younger sister) up until chapter 36. The rest of the female characters are the hackneyed "to be admired and protected, but rarely seen or heard" type, but Seoyeon's determination, eagerness, and aptitude in martial arts was refreshing.
It's not often you have a female character physically talented without her body being exploited for fanservice.
Then came the usual sexism - which was obviously disappointing after being spoiled(lol) by decent female characterization. The mother's character is wholly unremarkable and part for the course in terms of soft, genteel maternal figures in manga, and she is the one to ruin Seoyeon's character for me.
At chapter 36, her mother forces her to begin learning "feminine" things, like horticulture, cooking, and refreshments. At Seoyeon's understandable protests and insistence on continuing her physical training, their mother says, "You can, my daughter. You are a girl...be a girl even on the inside."
This, on its own, is irritatingly gender role restrictive and sexist, but worse in light of what the mother says to admonish the father about letting their son choose his own path in Chapter 5.
I'm speaking of when she says, "We should first respect his decision to pursue what he wants to." This is in response to the father seeming overexcited about his potential genius as a scholar (rather than a martial artist).
I will say that the female characterization is marginally better than what we normally see in vaguely historical fantasy manga/manhwa, but...
Well, chapter 36 was about when I dropped the series last time, in favor of Gosu, but hopefully I'll be glad to stick with it on the re-read.
Atm, would rate it about a 6 or 7?
Edit: glad I did a re-read, if only for the characterization and development of the main character. His personality is refreshing, too, in terms of shounen archetypes. He's jovial, but not an idiot, and friendly, but not a pervert. It's super fun to see him curbstomp his adversaries, too.