It's been a little while. But long enough of a while that this this list may not be comprehensive.
- Added a final level. Clearing that level is essentially the (non-100%) win condition.
Well, two final levels, really, depending on your version. In the full version, it's "The Gauntlet" and comes as the 111th level. In the free version, it's "The Fauxntlet" as level 31.
The prologue and endings are storyboarded but not fully programmed or triggered normally yet. They do exist, though.
Most of the level layouts have been made to "fit" their world better. Grass Land levels look more open and sprawling, Spooky Castle Land is claustrophopbic, Cold Land looks more like an arctic environment, Zed Land's got prominent borders, and so on. The levels are functionally exactly the same as they were before, meaning that the solutions haven't changed at all; they just look more fitting.
There are sidewalk chalk marks (such as arrows and circles) that you'll see from time to time. The gameplay is still very much "just try it and see what happens" and so these don't really give away solutions, but they'll nudge you a tiny bit at least in some of the early levels. 1-1 and 1-5 are good examples of how they're used.
Top priority will be figuring out how free+full will be offered: as F2P+DLC or demo+paid. Really depends on some Steam logistics.