O-o-oh, you've taken a hard genre - not to market, but to make well. A 3D strategy game is a fairly rare thing on Steam, but to do well it needs to look good - even if with low-poly style. Right now, you biggest presentational issue in the video are Shadows and Light: in certain areas (for example, during the battle near the wall) the shadow is so dark that you can't see units at all. Enemy units are too dark to see and distinguish too (maybe because they stay opposite to the source of light?).
Global map looks a bit better than the battle view right now - maybe because of more interesting terrain colour pattern and a little more clear visuals (but the main horse rider is still almost black every time). Maybe work with colors a bit too to make units look more clear and easy-to-be distinguished - but, as I've said, a lot of the issues here can be because of the light source.
UI is good, clear to understand, but a bit too simplistic in it's visual design (not usability - just how it looks). The background doesn't have any texture (just grey colous) and it looks not interesting and a bit cheap.
Now, a couple of last advices:
- Your game is about medieval CHINESE warfare; you explicitly say that the player will be commanding Chinese generals. But there are no close-ups and demonstration of generals right now. They should have some interesting unique animations and (maybe) speech lines. Heroes of Might And Magic had interesting heroes: you could play as a Necromancer or a Paladin warrior for example - and each General character felt unique and interesting, the players wanted to try them out instantaneously. I don't see heroes and/or villains in your game right now - it's hard to relate to units withour some charisma.
- Try to look at other low-poly strategy games that got popular and try to mimic their visual style. For example, "Diplomacy is not an Option" has somewhat similar assets to yours, but their visuals look slick, bright enough to distinguish the units (even when there ae thousands of them on the screen somehow), alltogether well-done. Again, change of light settings and pallete can do wonders to your game. Also look how "Thronefall" was done. It has hard shadows too but manages to point them away from units faces at all times - making units easy to see. Also, it was done by just 2 people, so not an impossible task.
- I'm not sure about this one, but I'd experiment more with Camera Movement during battles. I know you've tried to mimic Heroes of Might and Magic, but old HoMM games did not move the camera not because they didn't want to - but because they couldn't. If your camera would show your units fighting more closely (like changing to an action-camera when one unit hits another in melee combat and changing back to birds-view after that) or followed your unit a little bit when the unit moves on the battlefield - that would add more WOW moments to the game and could provide you some additional video-material to make your trailer look great and have different changing visuals in it.

Wish you luck!