Those who talk to me regularly or pay attention to my lists will notice that one of the VNs that comes up fairly often is Draculius.
This is a VN that has had a surprising amount of influence on modern VNs... or rather, the Western VN world. Oddly enough, that influence is mostly indirect rather than direct (it isn't translated, so the VN's direct influence is rather limited).
The most obvious point is Grisaia... to be straight about it, it had the same writer as the Grisaia series, a fact that made me nod in recognition when I discovered it. Replaying Draculius, the points of connection are blatantly obvious... such as the fact that Misao's basic character is obviously the prototype for Makina or that Rian's characterization was the prototype for Michiru (though honestly, she is better than Michiru, lol). Zeno is Sachi's prototype (think if you added insane protectiveness and a tendency toward violence to Sachi and removed the good girl obsession). Last of all, Rika is Yumiko (except that the dependence comes out faster and Rika is a lot less weak-willed under the surface). It looks like Belche got split into multiple characters, probably because her role and characterization was so complex that building on her as is just wasn't possible (Amane, JB, and Chizuru).
Now, do I even have to mention how much influence Grisaia has had on the Western community? I'd be preaching to the choir at this point, I think.
A less-obvious point is Kyuuketsuki no Libra or Libra of the Vampire Princess, which is getting a localization through a Kickstarter sometime this year. To someone who played and loved Draculius, the older VN's influence on Libra is extremely obvious... Iris, who serves as an antagonist in the VN, is to some degree based on Belche (right down to her attitude toward humans and tendency toward obsessive love hidden under a cold exterior). The actual situation is a dead copy (play on Belche's special power, for those who have read the VN, lol) in the sense that both Jun in Draculius and the protagonist of Libra are young men who are the children of born vampires who died, leaving the child's mother behind, who then died before the story began. There are a number of differences of course... and I won't spoil the VN by telling you where a lot of the deeper similarities are (though I will give you a hint... the truth about the vampire hunter organizations).
Other than Dies Irae, I honestly can't think of a VN that has had more impact on the community without actually being translated, and as I re-read this VN for the third time, I find more and more common points with the VNs that came later on, lol.