Fantastic game! It's the most polished and up-to-commercial-standards game in its genre. Sure, it's a bit simplistic take on a Castlevania game. And it doesn't have much in terms of gameplay variety (only 1 weapon type and only 2 spells you get from the very start of the game), but what it has—it works well and makes for an immersive and satisfying game.
It would be a solid one even without the sexual content, which is something I can very rarely say about any of the games on this site.
That is to say, the sexual content is not (or not only) what makes this game worth playing.
But the said content is nevertheless amazing.
It's brutal. There is some guro stuff (which I don't like all that much, personally, but it does fit very well with the game style so I didn't mind it), and whatever sexual content is present in the game, it's all violent and non-consensual.
There are no tone-deaf comic reliefs around every corner to "lighten the mood". Or clowning characters with stupid personality traits like "Oh, she has a soft spot for cookies and sweets! Look how cute our heroine is when she isn't getting gangbanged by pigs!"
No, this game is a misery porn played completely straight. Bleak and depressing all throughout. Which is great for me. If not for you, you can treat it like a horror game, I guess, and be afraid to lose to the monsters or whatever.
Also, for once, in the game with sexual content mostly (but not limited to) on defeat, this game is actually balanced around it and doesn't require you to stop pressing buttons and stand there to get effed. It will most likely naturally happen quite a few times even if you play like a normal person.
Overall, this game is without question a 5/5 for me and has earned its place among my favorites.
I wish there were more games like this and with such high quality. But, unfortunately, save for this game's prequel, I can only think of one other game that is of comparable quality. And even that one loses the comparison, even though I like it too.
The review guidelines state I can't mention it, so I won't. But if you like this kind of stuff, you definitely heard of it at the very least. Sinisistar 2 is, in my opinion, better in most ways and is definitely the more polished one between the two. It's probably going to be many-many years before we get a game like this again, if ever. And this makes me sad, really.