@EddieK True honest, assessment.. it looks like a bad prototype made by a programmer, and here is what you can do to help it when you are ready to focus on that part. Look in Summary: The assets look like bad, cheap prefabs. That said, don't despair you have plenty of time to develop the art assets once you have the gameplay where you want it. I believe it is terrific to work with placeholders until you have custom art, and it just seems to be where you are at, so don't sweat it.
1. Textures: The current ones look like they have multiple themes and styles to them. You will want to work with someone to help nail down a consistent look and feel of what you have in mind, and maybe recruit a seasoned 3D/Modeler and texture to beef up the polish. Right now the textures are also super bland and generic, like a freebie repository download. I would suggest looking at some sort of low poly style if you can't find an artist to assist you. This way you can do some super low poly models and do colors on material fields and let post processing help give it polish.
2. Scale: When I look at it I can't help but feel that the squares look like small turrets too big, and trucks look shrank down like ants. You could easily scale up your trucks to make them look more appropriate to size. While you are at it, make the turrets take up 90% of the square vs 35%. I know I just sounded like I contradicted myself, however, the point is you have too much negative space and not enough positive space in your scene. Which is making it look empty and dead!
3. User Interface: It makes me cringe, cause it mostly isn't there, and what is there well, frankly, looks like once again something done by a programmer without artistic experience. A simple and consistent font will go a long way with any text! Try to keep it uniform throughout all elements. Icons eventually can be the actual models themselves that are screenshots of your assets with a transparent background.
Conclusion: it is far too early for you to worry about the cosmetics and what random butthole on Reddit has to say about your game. So what if it looks bad now. Nearly all games look like crap in the beginning, unless they are done by an artist, and then they just look pretty and play like a bag of crap, lol!
You gotta remember 80% of the internet is pretty much full of toxic critics that probably hate their own lives and everyone around them. So right now appreciate the 20% here to help you, and as you progress that number will swap places and that is how you know you are ready to launch.
Best of Luck, pm me if you need more help ^^