There is a 99 cent upgrade to activate other themes and remove ads.
Only short words available.
For a 99 cent upgrade you can purchase medium and long words, it will also remove ads.
I am not a fan of game apps that advertise as free, and then only give you a portion of the game. Just charge 1.99 for the game and make it awesome. No ads, all the themes and extras. After playing a few rounds of 4 letter words I was rather bored.