Grand Duke is a 3.5 to 4.0 stars experience for me as I'm no fan of the Koikatsu art style. However in the interest of being objective and setting aside personal preference, it's worth 4.5 stars. Essentially this is an AVN with a high potential story as well as interesting characters.
Story
MC got isekaied to a medieval fantasy world as an heir to the Valeran Grand Duchy. He is then tasked by the old gods to set up his own religion and amass enough devotees to become a supreme being in order to fend off evil forces from his realm.
The story isn't original, but the way characters are built, the detail in which the story world is unfolded as well as the reasonable interpersonal interactions given the circumstances does make the whole setup far better than the competition.
Unfortunately, GDV commits the cardinal sin of information overload at the start. Players are swarmed with an info dump which they have no way of processing early in the game. For e.g. the world geopolitics, Valeran Duchy history, different classes of knights, their powers and lifespan, past history of MC's body etc. are downloaded on players within the prologue and first chapter.
This is a common mistake by narrators who want to "get it done with ASAP" so they can move on to the main story, but players in the initial exploratory phase are often left in a state of confusion neither knowing what these pieces of information mean nor their relevance to the MC and story. I suggest the developer breakdown this huge chunk of information into digestible snippets and weave them into the story as it develops.
Game Mechanic
So far GDV appears to be a kinetic novel with occasional peripheral choices.
Background / Character Renders
Both backgrounds and characters follow the Koikatsu style which I don't really like as my personal preference is towards more conventional 2D anime.
Most of the background renders are around the castle and we have seen four LIs and some other minor characters as well. A thumbs up for actually having everyone including minor antagonists well illustrated, there is no cutting corners by using colored shadows or third-party narration.
The developer plans to craft a long and extensive story, so we can expect the introduction of many new characters and venues in the future.
Character Development
This is where GDV differentiates itself - all the characters from MC, the LIs to the supporting cast behave rationally as one would expect given the circumstances. This greatly aids in the immersion and my getting invested in each of them.
For e.g. upon waking up in his new body, the iseikaied MC takes time to retrieve the previous owner's memories, assess his surroundings, bid his time by blending into the new world and cover any tracks that he is no longer the same person. This in contrast to many other moronic iseikaied MCs who do stupid things drawing attention in a totally unknown environment from day one.
The same goes for his personal servant Eleanor - she mildly suspects there is something not quite right with the MC, but chooses to observe him for some time before eventually accepting the change could be due to the MC's life and death experience. This is the sort of detailed character development that makes GDV stand out.
On Ariana's appearance, I groaned in exasperation as she looked like a tsundere trope. But surprisingly, Ariana though unimpressed with the MC followed protocol as is required of a lower ranking noble. When MC helped her to solicit higher compensation for common soldiers, she exhibited a reasonable change in disposition. No sudden "I love MC' or tsundere "don't think this changes anything" nonsense here either, her reaction was convincing and totally expected.
Ditto the antagonist nobleman who is no fool and by piecing pieces of information he knows about the MC reached a logical conclusion that MC is likely faking his vanity during the meeting.
Sex Scenes
As of V0.25 Chapter 5, there is only one sex scene which is nicely animated with multiple angles and good enough dialogue. If standards can be maintained or improved, GDV is in good stead.
BGM and Sound Effects
The BGMs are mostly pleasant complimentary tunes that blend well and sound effects are minimal currently.
Conclusion
Grand Duke would have been my ideal game if it adopted a conventional anime or VAM / HS2 art style, but the fact that I still want to follow up with its development despite a personal distaste for Koikatsu is strong testament to the quality of its story writing and character building.
This is a must try for those who like this kind of graphic rendering style and worth a try even for others who are not impressed with Koikatsu.