To start with Solo Levelling sets itself up to be a series where we watch our protagonist Jin-Woo grow stronger by using his 'level up' ability. It's clear that it's just going to be a power fantasy, which is fine. The fundamental problem is that the story, world and characters are totally bland and uncompelling which is why I dropped this series after around 100 chapters. I don't care how powerful Jin-Woo is because cool fights don't make me want to read hundreds of chapters of a series. Cool fights get old really fast when you know what the outcome is always going to be and there's nothing else interesting about them.
Before we get into that, I'll note the only good things about this series. It's got good art. You can't deny that so I won't try. People overemphasize how good it is, but it's definitely good. The premise itself is also interesting and reminds me of another isekai 'So I'm a Spider, So What?', where in that series we would watch our protagonist using their unique videogame abilities to analyse the world and carefully plan every move so that they can defeat enemies and grow stronger.
Solo levelling isn't about these kind of interesting tactical fights because our main character goes from underdog to god very quickly. It felt like the series blew it's load super quickly because every character they introduced as being super strong became irrelevant compared to Jin-Woo by chapter 100. Regardless, our protagonist also changes his personality at some point from this nice but weak guy to edgy loner that everyone wants to fuck. It's confusing because it's not like he watches someone he loves die, he just becomes like this because he's strong. Maybe it makes some sense that he'd become detached given that he's a god however that really isn't fun to read because he's just boring now. What's his goal? He's already strong, so I guess become stronger.
The fact that Jin-Woo doesn't have an interesting goal is a big problem because fights are usually meant to be a clash of viewpoints between two characters. When all our character desires is to be stronger then the fights lose any potential emotional weight. The villains he's fighting most of the time are also basically robots (it's implied that the enemies in gates are being controlled by someone, so they have no real reason to kill people other than that they are being forced to), so it's not interesting on that front either.
The series eludes to the interesting point about how these god-like S tier hunters get to exist above the law and how maintaining order requires one guild to have a larger amount of S tiers. This gets forgotten about because Jin-Woo is stronger than S tiers so now we start seeing national level hunters talked about instead. There's an opportunity to explore the interesting politics of this world but instead we get to see chad thundercock Jin-Woo beat things up in different ways.
So we have a boring protagonist and a boring world for him fight in. There's an overarching plotline forming throughout which is going to explain what gates are or whatever, but I just don't see any reason it would be interesting. And I guess that's about it. There are some stupid plots to talk about maybe, though mostly I just don't like Jin-Woo. He's an edge lord but without an interesting reason to be one. We find out about his ill mum like 60 chapters in I think and he fixes that almost immediately. Overall, just a terrible manhwa.
