For Dev Update #5 the focus was on optimization, a new area, the water shader, and some minor (but nonetheless important) improvements.
So there was quite some stuff going on under the hood this time around. Even though the game should not be too taxing anyway, now stuff only gets drawn, whenever it can be visible to the player. Everything else will not be drawn, which results in a much better performance.
Also, there were lots and lots of code optimization, which should help going forward.