Being based on Ubuntu, Mint is sometimes hard to differentiate from Ubuntu or shed the 'Ubuntu plus codecs' image. But Mint is more than that. Mint tries to get as much working out of the box as possible. This includes codecs, Java Flash, online media, wireless, etc. Also Mint tries to fix some bugs which are usually bad default configurations in default Ubuntu... or at least provide an easy way to configure things properly.
Then there are the Mint tools. mintMenu is leaps and bounds ahead of the default Gnome menu... and with the Gloria, I think people will sit up and take notice. It is really the way a modern menu should be done (though not perfect... I don't like that you have to scroll in the menu). Think of searching in the menu for an application and if it is not installed... the menu offering to search and/or install the application for you! It's 2009! That's the way it should be!
mintInstall is another great tool... also not perfect (I don't like that it opens a whole lot of windows and dialogs). The .mint files provide the packager with many more options than simply a GUI for apt. It is a really good tool and I think would be a great model to follow for commercial applications in Linux that don't want to build a ton of packages for all the different Linux distros.
Many aspects seem trivial for most seasoned Linux users. But for those who are new or not as technically inclined, having almost everything work out of the box is wonderful. Even for Linux veterans, it is great to know that certain things will just work... so you can get to what you want to do much faster. This is what brought me to Mint from Ubuntu. Now, being part of the team I see why it is so. The standard required by anything released under the Mint banner is very very high. And that guarantees quality which seems to be lacking in some ways in Ubuntu.
Ubuntu has some flaws... but if Mint is great, we are standing on the shoulders of giants.