That's a really nice demo.
The basics of an RTS game are covered in it very well. I might want to use it as a starting point if I ever get myself to make a strategy game

Some minor problems I had with it (mostly graphical so they don't matter):
- Having the action and the select on the same button results in pretty interesting control. I might be conservative but the standard RTS controls should do fine here (Left Mouse Buton being the select and Right Mouse Button being the action)
- Some problems with the selection after a unit is created.
- Interface goes behind the units
- Text is sometimes barely readable.
- Sometimes the healthbar thing remains behind after a unit is killed.
The things I found very well done on top of the basic mechanics:
- Movement and animations are mostly fluid
- Auto-Attack is a nice touch.
I see that some of the graphics are from StarCraft and Dune. The other game I don't recognize.
Creepers are capable of climbing ladders, despite lacking arms. (Minecraft wiki)