This is neat! I found it a little difficult to get started, though: it took me a while to realise that "type the words on screen" were actually the words I needed to type right then. (My first guess was "SPEED" since it was sitting up at the top of the screen, and not immediately obvious it was connected to the slider next to it.)
Also, my score at the end showed as 0wpm, which seems as though it was probably wrong even if the average was brought way down by a long time spent blundering about at the start. I'm not that fussed, though: it's a fun game in its own right co competing for a high score would just be a cherry on top.