Sigh of the Abyss feels like a world bible turned demo that someone worked on in an inspired frenzy until they realized they had to make the rest of the game and quickly ran out of enthusiasm and ideas. The beginning feels fleshed out. Interactions are fulfilling, until about a third of the way through, then scenes begin to feel like the writer's half finished chore. Pacing is nonexistent as the story will repeatedly slam on the brakes so you can walk from one scene to do nothing to another scene to also do nothing. There is an unnatural aversion to any sort of genuine conflict or pay off in this. Endings are bland and anticlimactic despite the apocalyptic/revolutionary tone.
As for romance, it feels like a weak and tacked on afterthought. I imagine the female love interests fare better as you spend the most time with them and their character development is more closely tied to the plot of the story, but for the men, attraction is anemic at best, nonsense at worst. You don't even see one of the male love interests until well into the middle of the game and at that point your choosing him is based entirely on one or two short conversations.
For a dev who has made sexually explicit games in the past, this one seems embarrassed by any kind of physical contact. For example, some fetishes are brought up in Malec's route but the way it's expressed is a toothless afterthought. That same route, it's implied (not directly mentioned) that you've slept with him several times but only get his kiss CG at the very end of the game which is an interesting choice to say the least. There are otome/amare games that handle these things with confidence, even if employing a fade to black scheme, so this isn't a problem with the genre itself, but rather the writer.
I imagine, pitted against the average nukige on this website, the writing will seem sophisticated. But if you spend any time playing story-heavy or otome VNs, this will feel like eating a creampuff someone forgot to fill. The first bite will be fine, but soon you'll find out just how hollow it is.