I actually watched this series 3 years ago but this is the first time I write review about it.
If anything makes me like this series then it must be the build up, the tension between protagonist and antagonist is really high and pretty interesting, it makes the audience wonder how the series would go on. Sadly after that episode when Ahn Bo Hyun's character went to jail everything falls apart. The timeskip helped nothing, it just made the story more goofy and unrealistic, such as how in just few years the company of Park Saeroyi became a successfull one with the leader who is only around 23 years old, my gosh even Elon Musk couldn't pull that off. After that you get to see all the cliche of a kdrama like: Villians got cancer, kidnapping, a bribing proof from single person (Kwon Nara's character) lead to the collapse of an empire, MC wins just by luck, .... I mean seriously what did Park Saeroyi do so far, his plan failed after episode 9 and the rest is just pure luck that helped him win, this is what I call bad execution from a great build up and it happened because the crew were rushing to finish the series in 16 episodes, I believe this series could have been better, have they extended it to more than 16 episodes.
Actingwise I was impressed mostly by the villians, the father and son (Ahn Bo Hyun) played really well their roles, while Park Seo Joon had one of the most boring character in his career, he was totally outshined by Kim Dami, Kwon Nara was meh, not bad but also nothing special.
The music is actually the highlight of the series, even when the series turned so bad the music still got me, Itaewon Class is a series about young people and the music boosted the theme perfectly, I got hyped just by hearing the song.
Overall it's a mediocre kdrama with some spotlights in early episodes but crashed badly after episode 9, it's not worth of rewatching but it's still worth of recommending.