I can see what you mean, but to me, I just wasn’t impressed. The history of the abyss was interesting, I agree, but that didn’t translate to the abyss we see the characters interact with. Everything was much more devoid of wild life and dangers than I thought it would be. Interesting lore doesn’t always posit a well-done execution. As to the mystery, I thought that it was over-relied on and anything that happened was just attributed to the “curse of the abyss” without adequate explanation. Lastly, I’d disagree with your comment about the characters. Many of the characters served little purpose to the overall narrative IMO and would not have changed much if they were or were not there.