Ubuntu's largest flaw is the lack of a clean installer. Users are required to partition drives and configure settings through a slightly dated Ncurses (text) based interface. Displaying concise feedback to the user during install would ease the process. Even if you only have to install once, a clean and less verbose installer is necessary when usability is a main goal.
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Ubuntu has created an extremely pleasing desktop environment. Once the install is finished (only an issue for an unexperienced user) the system itself performs very well. Default applications and preferences have been thought out to make the user instantly productive. People looking for a Debian based system or new Linux users wanting to “get into” it will find this an excellent desktop OS.