Mambo is superior to other cms because of how it is build. While most cms focus on adding extra functionality in the cms itself; Mambo has created build in systems which makes it extremely handy for developers. So there are lot's of classes which a developer can use to create components and modules. That's why the amount of mambo software is growing so fast.
But also the install system for the administration is extremely powerful. Just some clicks and a component and/or module is installed.
When Mambo 5 will be released it will even use XML/RPC to distribute content to several sites at once. Imaging you have 3 sites with each a different focus but you want to display some info on all 3. It will be possible!
And last but not least: mambots! Mambots are very small programs which alters the way your sections work. So they can display images, thumbnails, links, whatever in your articles just by using a keyword like {mosimage}.
And I am sure I have forgotten lots of other good points
