I enjoyed the novel as well, but a reader of plenty of classics and let's just say it in simpler terms, a dedicated bookworm, it's definitely not on par with novels that are characterized literature masterpieces (art). The metaphors and 'symbolism' were in my opinion, mediocre and certainly not something i haven't seen in plenty of other novels before. The storytelling was definitely good, including the dramatic undertones(my favorite parts). But no, I wouldn't consider that this novel has as a requirement to be enjoyed, the ability to 'comprehend notions at a mature level'. If anything, it simply requires you to have a preference and tolerance to morally ambiguous characters, which once again is connected to personal limits and preferences. I can see why certain people wouldn't be able to tolerate it and why some would.
Having a preference for it, wouldn't prove you were able to understand the 'hidden' metaphors or comprehend the 'meaning' better than those who don't have a preference for it, this take would be very condescending and the result of a truly dichotomous, close minded point of view (just to be clear, I'm not saying this for you, I'm speaking in general terms). Someone can take into account every detail, every literary abstraction, including symbolisms and 'feelings' but still simply, dislike it. Taste is simply taste, and as i see it, no taste is superior to another. That's all, sorry for the rant!

just to preface to anyone that hates the story, this WEBTOON isn’t meant to be your typical romance, if anything it’s on par with being a piece of literature art with hidden metaphors and underlying meanings throughout (especially in the novel) so if it’s not your cup of tea, I’d advise not to read further but if you’re able to comprehend notions at a mature level, keep reading it!!