Windows 7 or above. Not entirely potato-friendly (yet).
Toggling fullscreen on and off seems to help when the game runs slow.
Past the big dark tunnel (same place where the first demo ends) there is very little to do at the moment: the in-structure puzzles are non-operational. Optional platforming challenges (the open air ones) should function, however. Still, I don't recommend wasting time exploring past the tunnel yet: approximately first 50% of the game world is in this build without its main ingredient.
Also, past the aforementioned end of the original demo (the big dark tunnel) the music switching system is broken / not set up (because there is no more music at the moment). Technically you can keep playing if you turn it off.