Last official update here, and moving forward I'll post all fixes / changes in the game DevLog.
A couple of people advised me that the download was not working. It seemed to be an issue with the zip archive (probably the settings I used). I re-upped as a single executable.
Also, in chasing down an issue that was causing a black screen when going fullscreen (Alt-Enter), I managed to get the game to run at an excessive CPU load. I found that I had enabled both vsync and the "alternate vsync method" in GameMaker. Turned out only vsync was needed to correct the fullscreen issue. The alternate sync method was tripling / quadrupling the CPU load. The more you know...
In any case, it appears to be working as intended now.
Good luck to everyone else!