As the final non-LTS release before Lucid Lynx in April, Karmic is heavy on new features--which are likely to be less pronounced in Ubuntu 10.04, where Canonical will concentrate on stability and performance.
AestheticsFirst, in the look-and-feel department, Karmic will feature a new theme and icons, as well as a flashier and more elegant gdm login manager. These changes are a beginning to the aesthetic overhaul that has been promised for some time, and will hopefully continue with future releases.
NetworkManager has also received a facelift, with new icons and animations.
New appsProbably the most visible addition to the default application stack is Ubuntu One. Also noticeable is the replacement of the instant-messaging client Pidgin with Empathy, a decision marked by more than a little controversy among users and developers. I concluded from my own comparison of Pidgin and Empathy that the differences between them are negligible for most people, and those up in arms over the change should calm down.
The Ubuntu Software Center, called the "Software Store" in earlier iterations but renamed after a debate among developers, will also debut with Karmic.
Finally, a slideshow now accompanies the ubiquity Ubuntu installer to provide new users an overview of their system.
Stuff for geeksFor geeks, new applications and utilities include the Grub 2 bootloader, kernel mode setting on Intel chipsets, and a more sophisticated command-not-found hook in the bash shell. And Ubuntu 9.10 will deliver faster boot performance. None of these changes is likely to matter much to your grandmother, but they're cool all the same.
Also appearing with Karmic is a utility to diagnose how well Ubuntu will run on a given computer, which is something everyone can appreciate.
Will all these changes position Ubuntu 9.10 to compete with Windows 7, which has just been released? Only time will tell.