This game has a really good underlying foundation, the UI needs improving though: I recommend you familiriaze yourself with CSS and HTML so you can style the UI to your heart's content.
It's not very clear at the start of the game whether the wave system even works or not, it should say Intermission when it's wave 0.
More towers and content in general would be good.
Oh and there was this error being spammed:
[Generic] Exception when calling 'Update' on Player
System.NullReferenceException: Object reference not set to an instance of an object.
at Player.OnUpdate() in Player/Player.cs:line 87
at Sandbox.Component.InternalUpdate()
GameplayMultiplayerControlsUnfinishedErrors