I first want to congratulate UW on making such a gorgeous and fun to play game. You guys took a bland (but addictive) game and spiced it up. But I wanted to make a quick suggestion of adding an optional solution timer that tracks and possibly logs your best & avg solution times for different difficulty levels. I've seen this on web-based games and can be kinda fun to race yourself.
Sorry if this has already been suggested (or if this isn't the right place for such discussion), it's late and I want to play one more game before bed