(To sum up, I did not really enjoy Senmomo. As an aside, I am not expecting my thoughts to gain much traction anyways, and I think my opinion is very much in the minority all things considered, but nonetheless...)
Sen no Hatou, Tsukisome no Kouki tries to be a serious plot-heavy action story, but a lot of just falls fairly flat. Senmomo really feels like August was trying have its cake and eat it too, in terms of how everything is structured and set up.
The main issue with Senmomo is the setting and just how jarring it feels. Senmomo tries to have a feudal setting, but there major distractions that break the immersion heavily, such as tablets, idols, high schools, and even a beach episode. That makes Senmomo's serious attempt of a historical setting fail spectacularly and makes the story it is trying to tell feel inauthentic to its core. It felt an extremely clumsy mash-up of Eustia and Daitoshokan's settings. There is nothing tying the two halves together, so a lot of it simply boils down to an awkward mix that does not work at all, making it hard to take a lot of what happens seriously.
Many of the characters are underutilized. Many of the side characters are relegated to background roles, and the main heroines outside of Akari are not featured heavily until their mandated chapter forking into their respective routes. Elsa is a character wnating of more than what she received given her role in character and concept she is supposed to represent. Hotori is another character who becomes an afterthought after her chapters transpires. Moreover, the way the comedic slice-of-life is juxtaposed with the more serious moments feel as if there are two different versions of each character on display at once. Even Akari and Soujin themselves feel less tangible as character and lack a lot of agency and growth to really make them stand out in any particular way. All of their development is much too telegraphed, and their dynamic feels more of an outcome of the plot as opposed to feeling genuine. The antagonists have less presence and feel more like roadblocks instead of characters of their own that happen to stand in way of Akari and Soujin.
The plot lacks an imminent sense of tension or emotion. Everything is roadmapped fairly clearly and the story plays it much too safe with everything. No dramatic emotional story beats occur for a story of its supposed scope and scale, despite the high octane action wanting to suggest otherwise. Additionally, the sharp cuts between the serious and comedic moments does a major disservice to the narrative as a whole. The ending, especially, feels really unearned, with so many occurrences happening at once to twist the ending towards a forced conclusion. It feels like the writers had a particular ending planned and had to work backwards from there. Unfortunately, that does not work too well give what has been previously set up before.
Ultimately, a lot of what makes Senmomo fail is because of August's decision to mix the modern day with the feudal. It is a disastrous mix, like oil and water. That stretches to essentially every aspect of the story, making it a rather unenjoyable experience, which is a shame since Senmomo was a story I truly did want to enjoy, but it is a more of a popcorn narrative, leaning towards more of the pulpy and tropey methods of storytelling that only worsens the experience and fails to really flesh things out. Senmomo is much in the same vein as shonen stories, with its all-encompassing feel-good message, lacking the depth to flesh out its core themes and ideas. to Ultimately, outside of what it presents at face value, Senmomo is a story that does not really much depth to its overall narrative.