Having the space bar slow the character down really threw me off which admittedly because its not something I've seen before which is a good thing! Such a simple concept but kept me coming back for more; the grey blocks were too tough for me wee mind so unsure what else was lying it wait.
My design mind already sees other thing this game could add such as blocks that speed up or slow down alongside Billy himself slowing down to throw the player off; love the fact that your way to use the one button leaves so many options for exploration open.
Will say that at the beginning of the game the scene jolts as from what I can see Billy is started at too high a Y position? May be wrong but is noticeable when the rest of the game runs smooth. Plus some sort of progress gauge is nice, I would have likely kept playing if I knew there was more waiting.