Really cool concept, however it felt more like rote memorization than a game. Memory games are fun, but with this game it is basically trial-and-error for the first while before you begin to catch on (at which point it becomes more engaging). Perhaps you could introduce short words with similar letters early on to practice some core letters before adding new ones which must be discovered? This would lead to developing muscle memory sooner and I think would have more of that "Aha" feeling. Additionally, I feel like a visual on screen keyboard layout could have been a kinder addition, and the WPM feature could be more of a focus for the "score".
The graphics and audio were very well fitting, and with a few gameplay touch-ups this could be a really cool and fun game. It's almost there, but its more frustrating than rewarding at the current state.
Good job! This is a really strong submission.