The differences aren't so obvious at first, however, you do start to notice the improvements from the newer, better block design and snapping methods, as well as the new placement of things the "Pallet" which boosts some of the user friendliness of Stencyl. It's subtle but definitely there. After that, there are other improvements which I have yet to explore.
Looking good so far. I heard the completed 3.4 version will contain better documentation of every block too?