Synaptic is an extremely popular and feature rich package manager for Debian based systems. What sets it apart from other package managers is the ease of use, features and stability. Synaptic Package Manager can execute almost every task that can be done via apt-get command. However, since it was build on Gtk2 it doesn't fit very well with 'newer' Gnome 3 systems. Especially if you are using Kubuntu then Synaptic Package Manager is an eye sore. The good news is developers have updated the UI and ported it to GTK3. After this update, Synaptic Package manager will look more native in Gnome shell and Gnome 3 based desktop environments.
Andrew of the popular Ubuntu blog WebUpd8 has uploaded the code in his PPA which makes it easier to users to install it on their system.
To install this update in Ubuntu, you will need to add a PPA (as it is not an official PPA and it's still in unstable stage, expect some bugs and surprises).
sudo add-apt-repository ppa:webupd8team/unstable
sudo apt-get update
sudo apt-get install synaptic