The biggest difference is the affect on the global-namespace. It uses no global variables, and only the one global function. This makes it absurdly unlikely that it will conflict with any other scripts on a page.
Mine doesn't use the body or window onload events. Again, making it unlikely to clash with other scripts and making installation easier.
This one let's you have a carousel with an arbitrary number of side; the DD script only allows 4/6/8/12 sides.
In mine, I've tried to precompute as much as possible. The movement is done with a very fast update of the images' rights/lefts and widths, using values stored an array. The DD script does the same expensive floating point calcutions over and over, every 50ms, and constantly changes the src's of it's image element (necessitating more extensive DOM updates).
What else did I do? Hmm...