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 xx numbers of layouts, xxx numbers of sprites, tilebg, audio etc. to export every time when you want to preview it.