The thing about Art updates, is that they are going to be ongoing for a while.
The other thing about Art updates, is sometimes you are just overly stoked about an outline pixel shader you built.
That said, here is what you may find changed:

• Real hawt pixel outline shader
  
• The Manapult (man-a-pult? man-apult? minion flinger?) is here! Can you actually purchase it in game? Maybe. Can you actually get any minion stock to fling? Not sure about that either.
  
• Sharpeye and Softskin now with animations, including slash / shoot effects. Other, more cat-like, minions looking a bit broken.
  
• Animated Fire
  
• ManStations indicator on rooms display hud added
  
• Crystal Ball Room added. Currently only gets cooler at level 3.
  
• Autonomous units
  
• Huge updates on invaders in general
  
• Random events may spawn some invaders
  
• Running away from battle doesn't give you double money (oops)
  
• Fires don't remember being killed anymore, so they will flare up at full strength
  
• Gates now color according to level
  
• Player castle is fully programmatically displayed (for now)
  
• Huge general UI update
  
• Shields are arguably much cooler