On request of the author I added a new addon plugin for NextGEN Gallery and Monoslideshow. It’s a flash based slideshow with amazing transition effects and more over you can customize the slideshow in nearly all aspects. I’ve added a option to replace the default slideshow of NextGEN Gallery, so you didn’t need to update your posts/pages. It’s currently in a late beta stage, where not all features ready (Custom presets), but you can work with it if you have owned the Monoslideshow. Leave a comment if you have a good idea what should be added to the plugin.
Download NextGEN Monoslideshow
Beta version @ wordpress.org