The entire end sequence of this game is basically, "Absolute Cinema" meme the entire time. The Grey Oni isn't anything special, but the final fight against the Black Oni is really neat.
That being said, I can imagine if you don't take the Counter/Guard technique, the end of the game is probably a LOT harder.
About the only real downside to the game I'd say is, honestly, its a shame there's only basically '2' endings, and I think its just down to a choice at the end. But I guess also making endings for each of the girls would be a bit much, and it would take a while to replay through the entire final sequence to see them.
The artstyle is really nice too, and the music they used is solid. The boss fights are all fun enough, and since there's no leveling you don't have to worry about trash mob fights either.
About the only h-scene I missed, that isn't a game over, is probably the maid's. I suspect you had to go somewhere before the Yellow Oni sequence starts to see it, but at least the Recollection Room works fine.
The translation is also fairly decent. There's a few times the translation turns back to the protagonist's canon name of Sousuke despite what you pick (and adds the 'e' vowel), and a few other times the translation suddenly refers to him as her but that's about it. Not sure anything is wrong enough to detract from the story though.
I'm not sure I'd say this is one of my overall favorites, but its a really solid game.