So this is going to be a fairly short review as I agree with so many of the criticisms already displayed by frustrated watchers about how this had potential to be amazing but ended up as a bit of an incoherent mess... (honestly it started off as a 9 for me then became a 6 after the messy ending).

THE STORY
So one thing I absolutely adore in fantasy stories is excellent world building. Or if there is a messy world, that there is enough information and good writing to make a suspension of disbelief bearable. I was unfortunately disappointed. From the beginning, it was called Abyss, so I wished that they'd explain more. Unlike what other people may have said, I actually really liked how the beginning started off running- with a death about a minute within. I liked how there was a thriller/mystery aspect that could keep me engaged, but it, unfortunately, turned into a bit of a W + Goblin plothole mess combined for me. I really wanted to love this, honestly. I love both the main actors but I just didn't feel this as much as I wished. The mystery started off strong but it felt like the writer ran out of ideas to make the villains smart so just dumbed down the characters. I also wish I saw more of the black coat people (were they a sort of grim reaper?) Like I said, so much potential but the writer focused on the wrong parts.

I think one of the biggest mistakes the writer made was focusing on the characters "doing this and this" for the plot to go on and just using the characters as a device to push the plot forward, without clear thoughts on the characters themselves and their growth.

One more thing: WHAT IS THE MISMATCH OF SCENES. Like there was so much seriousness going on in the latter half and the mains would go off alone on romantic dates like- okay unrealistic and it was jarring to have the scene shift from thriller to fluff right away.

THE CAST
So many people had a myriad of different things to say about the cast, so these are just my few pointers.

Ahn Hyo Seop is one of my newer favourite actors ( I loved him in Dr. Romantic) and I thought he did a pretty good job with what he was given. I was actually appreciating how he acted despite the weakly written character. I have not seen a protagonist this conflicting in character and kind of dumb in a while. Cha Min confused me a lot. He was smart that one time he had to talk to the board of directors in Lan Cosmetics, but then somehow jumped into trouble immediately looking for his ex fiancee. Where did his sanity go? Lots of people would say Hyo Seop was a little green- honestly, he did a good job for what he was given. If I was given the same character I would be so lost because there is zero consistency nor character development for me to build a coherent character off of. Perhaps with more experience he could have saved some scenes but I thought he did well for what he was given. It was a waste of potential.

Park Bo Young did pretty good in her portrayal of her character. Compared to Cha Min, Se Yun was actually more fleshed out in the script and her personality was more clear. I think Bo Young was a good choice (though I would not agree that she is a "plain jane" sort. I think she's really pretty and cute). I don't have much to say because her character was written with less problematic inconsistencies than Cha Min so it was a good portrayal.

The rest of the cast did well in their portrayals as well, and for once, I felt like a lot of the supporting characters actually were written better than the mains. The chemistry of the mains was really cute though and honestly their relationship moments saved some parts.

MUSIC
The music was good, the ost for their kisses was unique and had a wistful feel but honestly the script didn't set the mood. I loved the "Into the Abyss" OST though.

REWATCH VALUE
It's a 7 for me because of the ease of the plot and would be something I'd play in the background if I have time. It's easy access on Netflix and fairly chill so it's fine to kill time with.

CONCLUSION
Like I said, I think the major flaw here was the world building and script. There's another drama that Bo Young was in that I had similar views of (Strong Woman Do Bong Soon) but the cast was so loveable and the characters were not as conflicting so I ended up liking it a lot despite the plot holes. I think Abyss was a little over hyped by the production companies which lead to a lot of disappointment. The couple portions I think saved it but overall it's just a drama that I will just let pass by me with an "eh it was okay" moment.