Soul Cartel is a fairly straightforward action, adventure shounen webtoon in which the protagonists fight monsters while going from point A to point B. It doesn't really add anything new or interesting to the genre, but it's a pretty fun and light read on a slow day.
While I agree with the other commenters that the plot and characters are generic, I do honestly enjoy reading this series. Even if all the characters are flat caricatures, they actually fit the atmosphere of a (admittedly shallow) adventure series well. It's not a work that will change your opinion on a genre you dislike, but if you like this genre, Soul Cartel falls nicely within it. It definitely plays it safe, but it does so enjoyably enough that I don't entirely mind.
The worst part of the plot, though, is definitely Faust. Faust is, in a nutshell, perfection incarnated. He knows everything about what's going on, and he never risks defeat. He's probably the most powerful person in this entire webtoon, even more powerful than Mephisto (who actually seems to have trouble with some of his fights). He has such great plot armor that this plot armor basically extends to every single other person he comes in contact with, and so there's basically no tension at all when the "good guys" fight the "bad guys"." The good guys will obviously win because, after all, Faust is with them!
That's not to say that Faust is a dislikable character. No, he's just a bit of a disappointing character because there's so much potential (such as an exploration of the backstory of his current incarnation) that is overlooked or forgotten in favor of making Faust a super powerful figure with no weaknesses. Once you get past that initial disappointment, however, and accept Faust for what he is--an overpowered plot device--the scenes with him become far more enjoyable. And it even becomes kind of fun to guess precisely how Faust will utterly destroy his opponents this round.
The other characters have slightly more personality and development, though not much. They're all very shallow, but, as I said, they fit well into a plot that is also shallow, and the whole series isn't really meant to be taken that seriously. It's like one of those hollywood action blockbusters in that it isn't really about the plot or the characters, it's about the cool explosions.
But, if you tried out this series and didn't like the first few chapters, I wouldn't recommend continuing. It doesn't really get any better. It's a consistent series in that it never forgets what it is: a cheesy adventure series, and that might just be one of the main reasons I like it.