ability to preview as an EXE instead of through a web browser like with construct classic - one click and an exe appears running on the screen.
Yes, that is a "must have" feature. As I wrote in this post here running a game from an *.exe and from browser are two different things.
It's just a simple example but it's impossible to test it, cause in the browser that game is unplayable. So to test my game I have to export it to exe every time and it's only possible now, after releasing r100. I had to abandon that project before because I could not test it properly.
And it only a small, simple game - not even small just few tiles and sprites moving across the screen, and it takes about 5-8 seconds to export it.
Now imagine all that big projects, with ** numbers of layouts, *** numbers of sprites, tilebg, audio etc. to export every time when you want to preview it.