I have developed many puzzle games and card games with multiplayer mode. For such type of games is very important to have intuitive and funny user interface.
I know how to generate a grid of chars to emulate difficulties levels. Just for example: the following things may emulate difficulties levels in the game: crossing words, making words shorter, use rare used words.
What is entertain people more in such type of games are music, graphic and animation. I do not understand in music much, but I know resources with a lot of good free music.
I know many good examples of such games and we can take the best ideas to implement them in your game.