Disclaimer: I have played through at least one route of the otome game this manga is based off on. May have influenced this review slightly despite me not wanting to focus on it. Slight spoilers.
Story - 7
Geten no Hana, or Flower of the Human World, is a manga that takes us back to the days of Nobunaga Oda. The story is different from other things I have seen or read before. It has a unique premise, and the story is enjoyable. It does have a few cliches that one would be able to find in 'infiltration' centred storylines, but it doesn't detract in the story in any way. I mentioned earlier that this is based off an otome game, and as of writing this review, the manga's direction appears to be heading towards the neutral route, meaning the romance is not exactly skewered towards one character. The story is simple but it is the characters that makes it interesting. It's the interactions between Hotaru and the men of the castle that drive the plot and the actions of our main female protagonist.
For a short manga, the story is intriguing enough and has a definitive issue that pushes the characters forward. It also gives all of the guys a bit of the spotlight from time to time, so each of the male leads gets their own scene with Hotaru for a few pages at least once.
Art - 9
What can I say, Kumada Yuka's art is very nice to look at. It is very 'shoujo'-like, and it's smooth and clean, you'll never have any trouble trying to discern which character is which. There are also plenty of scenes that showcase the scenery, there's a certain one with lots of flowers that is very nice to look at. The volume covers are also pleasing to the eye. It's a shame that all the boys didn't get their own, but the ones that did - they look amazing!
Character - 6.5
I'm making this judgement excluding all that I know from the original game. They are less fleshed out in the manga, which I won't judge because it's already incredibly short. The characters are distinct enough in terms of personality, making each one stand out. Some of them are given brief moments of the spotlight to distinguish their personality even further but aside from this, they may come off as very flat because the manga does not explore any 'route' in particular - it takes the middle path, so the characters within the story are not explored. The only exception to this would probably be Nobunaga and Nobuchika but even then, I would say they are only about a step or two in front of the supporting cast.
However, putting this aside, I still think the characters are written well even with their lack of character exploration and/or development. Each character has their own motivations and dreams in terms of serving their lord, Nobunaga. Nobunaga's dream is given a spotlight of its own. It's their drive and I think the theme of having a dream is shown off well in Geten no Hana.
Although the story features a reverse harem, the main female lead is, for once, not useless! What a turn of events, she's a character that can handle other opponents. She actually has some skill of her own? Amazing! She bumps up the 6 to a 6.5.
Enjoyment - 7
I would have put up an 8 but I feel like it would be a biased answer. It was a good read, but not 'great'. It's something you could read over lunch and be happy about. It has a nice dash of romance (mainly with just one character but let's just skip that) and lots of cute guys to go around. Each and every guy is likeable in their own way and all of them have their quirks. I don't think I hated any of them, honestly speaking. Nobunaga is a bit amusing, Mitsuhide's antics with keeping up the facade of being her brother is hilarious, Hideyoshi is jolly, Ieyasu is sweet and shy, and Ranmaru (my favourite) is a little awkward but it's endearing.
If you like manga with pretty guys, or reverse harems with an actual not-useless main female lead, I recommend Geten no Hana. It has a light dusting of romance and a nice dash of suspense, tied up with lovable characters.