Yami to Hikari no Sanctuary is a game made back in 2017 that came very close to being my VN of the Year for that year, for good reason. Since I've already reviewed this game as a whole once, I'm going to go into more detail about what the catch points are of this game, as opposed to merely assessing it based on a lot of general points.
A major plus point of this game is the way Alice, the main heroine, often serves as a sounding board to provide the reader with an intellectual understanding of a situation. Alice, to be frank about it, is a straight-out genius with an incredibly strong will and a pragmatic personality. Throughout much of the story, she provides the reader with a better understanding of how the upper classes' culture works.
How is this important? It is important because this is one of the few games where people from extremely wealthy backgrounds interact in a non-idealized fashion (in other words, they aren't always straightforward and are willing to trap the characters with their words and actions). As an example of this, Claudette (one of the four main heroines) is constantly trying to trap Souji into giving her an opening to drag him into a romantic relationship. The wordplay is often used in a way that those unaccustomed to the customs of old money will find hard to interpret, and it is Alice's early explanations that provide the background to understand the byplay for scenes like this.
All the little bits of information and explanations that Alice gives along the way provide the reader with a deeper understanding of how the setting works, all without it feeling unnatural, because Alice is defined early on as what is known as an archetypical 'wiseman' character when it comes to social interactions.
Souji, on the other hand, is played as a contrast to Alice, as he is both socially inexperienced and seemingly 'normal' in personality... until the first time you get some background dropped on you or you see him fight (it is hard to get this across, but essentially he was trained to see fighting/killing monsters as mere routine work, like getting up in the morning and eating breakfast). Souji was raised to master 'Izumo Style', a martial art that requires the trainee to literally be trained as an infant (their limbs moved in particular ways even before they can walk) and grants the user incredible physical prowess. As an early example, without really trying, he can crack titanium body armor with his bare hands.
There is a rather large contrast between the extended common route/Alice's route and the other three heroine routes (partially because someone different wrote them). The extended common route/Alice's route is much more serious from beginning to end than the others, where more time is spent on mundane activities. For those who merely want to experience the story, I recommend just playing Alice's route, and for those who want something milder/more standard, I suggest playing the other heroine routes.
One thing I need to emphasize is that all the routes are very high-quality... which is something that is hard to do when you split responsibilities between two writers with distinct styles/tendencies. The consistency (internal consistency) between the routes is not perfect (one of the factors that went into me not picking it for VN of the Year that year), but it is consistent enough that I don't feel that anyone who plays the game will pick up on it without actively nitpicking.
The characters in this game are also very well-designed/characterized. Whether it is the two mains (Souji and Alice), the other heroines (Yuuri, Yurie, and Claudette), or the side characters (Joseph, Kisara, Saika, Noa, Noel, etc), they all have distinctive roles that fit in with their individual character backgrounds and personalities. In particular, I want to note that Saika (who is also a sub-heroine for a normal ending) has probably the second most influential position in the VN behind the two main characters (Alice and Souji). There is literally no path in the game that doesn't feel her influence to some extent, and it is this effective use of side-characters that often defines the difference between a second-rate writer and a first-rate writer.
One thing that bothered me both times I played this game was that Saika didn't have a separate route of her own. Yes, she often plays the antagonist, and her excessively manipulative nature makes her a hard fit in some ways for a Japanese visual novel. However, the degree to which her character is built up in the game made me fall in love with her to a degree that matched any of the main heroines, and it left me wishing the makers of this game had given her a better chance.
This game could have easily become a chuunige, with a few tweaks, and, in retrospect, I'm somewhat surprised that they didn't go that path, considering the setting. There are mysteries, a protagonist who is incredibly powerful, influential heroines with strong personalities, and individuals with ambiguous motives galore. That they didn't go down that road makes me feel somewhat wistful, as I would have liked to see Souji go all-out more than once in the entire VN (there is really only one fight where he goes all the way, and the results are splatter, lol).
Despite the often complex content of the story, the language of the narration is surprisingly easy to decipher, though it is definitely harder than the narration found in a charage. As such, I often find myself recommending it to people who want something serious but are new to playing untranslated visual novels.
Overall, this game has a lot to offer to someone who likes a lot of interesting details in their settings, while not becoming a game that is entirely dependent on the depth of that setting. It is also a game with a strong cast of characters and an interesting story... and in the end, that is pretty much all I want out of a visual novel, lol.