Open at Nine is a brothel simulator with some very nice animations and art but poor gameplay and story.
The core game loop consists of matching customers to girls then placing them into rooms. You get bonuses if the monster girls' race matches the customers preferences. Building rooms that suit each type of girl gives them stat bonuses. You can use consumables to temporarily buff their stats, allowing them to fully please each customer.
The problem with all this is there are just right and wrong choices and it's immediately obvious what they are. There's no difficulty, no learning curve, just match them up and hit go. You don't even get to see the customers work with the girls. It's brainless and boring.
Outside of the brothel, training consists of using items on the girls. That's it. No art, no scenes, just a voice line. I'm just as disappointed as you are.
There are scenes between the girls and the protagonist when they hit lust break points. The art and animations are quite good, but the girls and protagonist are soulless and obnoxious respectively.
Finally, the story is just boring. The protagonist accidentally blew up half the kingdom while killing the demon king and needs to pay back his debt by running a brothel. The protagonist can't decide whether he's a sex god, an unrepentant pervert, a repentant pervert, incompetent, competent or anything else. His character traits morph to be whatever is most convenient at any given time, making him pointlessly bland overall.
The girls are just as bad in their own ways. They're each one dimensional characters targeting a certain sex cliche, but barely bothering to develop it before fucking. For instance, the cat girl is a devoted companion (Or eye candy? Hero waffles on it.) who the hero deflowers then puts to work in the brothel in the same night. Despite her devotion, she apparently has no issues with this, nor does the hero. The story doesn't even really bother developing any sort of NTR vibe despite how low hanging that fruit is. All the stories are this soulless. As much as I prefer my brothel managers to be lighthearted and consensual, this is not the way.
I'm a huge fan of crunchy management games so I was pretty disappointed overall. Nevertheless, the art and animations are quite good and the gameplay is at least fairly quick despite being repetitive and boring. It still beats RPGM combat. If you like the sample images, it might be worth playing just to see the scenes, but don't expect a story or gameplay worth playing. There are a dozen better brothel managers on the site.