I've worked with many different CMS systems for the web.  I spent a lot of time in Dotnenuke and have worked with Typo3, Joomla, Mambo, Wordpress and many others.  I like to descibe them as 80% solutions.  Meaning it is really easy to make an "80%" great site in a very short amount of time.  The problem comes when you try to do something really amazing.  It is incredibly hard if not impossible.