The design is good, it's nice and simple. I like the concept too, it's quite different.
I would recommend adding instructions on how to use the wilds though, I had no idea they were even there until I read this thread and the W in the corner doesn't make it clear either. Also, what dictionary does it use? I tried to play "zoological" but it said it's an invalid word!
in regards to the dictionary, I am using Kevin's wordlist. Its the only free/open wordlist with all the stems and free... so you get what you pay for. "because" also doesnt work... Ill be updating as people tell me words that are unrecognized at each iteration.
Thanks for your feedback and playing my little game!