Holy crap dude. This is easily one of the best games I played, I loved every second of it and look forward to the next update. Huge Overlord fan (I've only watched the Dubbed version of the anime, which is awesome).
Multiple paths, plenty of women, and a brilliant storyline. I take it this is ripped directly from the Manga with some alterations? I noticed, for example, the scene with Shalltear being brainwashed was completely cut and replaced with a Dragon for some reason so I can't say with absolute certainty how accurate your visual novel is, not that I really care.
Yes, the game follows the LN as closely as possible while adding a few custom characters, scenes and of course hentai.
Other than that, it also features many choices which can also alter the main storyline... Facing the dragon (Catastrophe Dragon Lord) rather than a mind-controlled Shalltear is one such choice.
By sparing Clementine, Momonga no longer has the need to find a martial user, so Shalltear never looks for one.
That means the Black Scripture manages to get to the dragon and attempt to mind control it instead... And kind of fails to.
That is actually one of the most important choices in the game as it will affect other things as well... Such as Brita or Brain.
Other things were changed (such as the Dwarf Kingdom, or most of volume 14) to fit the ending I have in mind for Overlord H.
-edit-
For the most part, you can make the same choices as the canon material (kill Clementine, leave her body there, never pursue any woman, and so on).
Should play out the same way until around volume 14.