Version 13 mainly focuses on GUI. We tried to improve the clarity and easy of use. The GUIs themselves have been redesigned when appropriate and some related changes have been made:
There's a new style (Neon), which is enforced as default style and everything is designed to work well with this style "out of the box". This includes everything from basic components to various graphs and analyzers. Previous style settings are ignored now. If you feel the need to get your style settings back, it is not recommended, but you can hack the engine by going to the user settings folder (where the presets are) and copy StyleSettingsV11.cfg to StyleSettingsV13.cfg in proper folders. Note that other styles may not work that well compared to Neon. While we are going to slowly improve other styles as well, it has a low priority. Neon is the new "look" of Melda plugins.
Sliders/knobs/buttons option has been removed and all plugins now use a combination of all 3. This way we can optimize the layout to make it work well, resize only if needed and look clean and easy to use.
Plugin toolbar is now collapsed by default. While it is one click away, the default can be changed in Settings. Many details such as knob response times to dragging / mouse wheel have been standardized for faster workflow. Style engine has been improved and so has the style editor. While older styles are still compatible with the new version, they probably won't perform well enough. New styles cannot be used with older versions of the plugins.