Better layer system, More clear info on what things do, ability to rotate doors, Better HP system bit less punishing when you clip through the wall, more Buildings maybe a better lay out to the current buildings,upgrades for windows and doors could be neat.
For layers maybe make the repair orbs always be on top.
More clear info on stuff and explain what and how it works, like blue orb i have no clue how to use it what it does and how.
Maybe give the player a build able that warps you to it on getting hit as a back up life.
A sell circle to go with the buy circle,maybe a shelf that you can consolidate all your money trees, more trap types.
For lay out you could organize it better and make it easier to pick with all similar buildings being up and down from each other and each building group left and right of each other.
A ability to upgrade everything to its next tier, and upgrade windows and doors to like barred windows and metal doors, Upgrading traps would bring them up a tier same for barricades.
That would probably get it going in the right direction it feels really good as is for what it is. so a bit of polish and more content will go a long way.
Also this Custom text still amazes me.