With the latest release the Wireshark Project decided to make the Qt GUI the default interface. In line with Debian’s Policy the packages shipped by Debian also switched the default GUI to minimize the difference from upstream. The GTK+ interface which was the previous default is still available from the wireshark-gtk package.
update: Wireshark 2.0.0 will be available from testing and jessie-backports in a week. Ubuntu users can already download binary packages from the Wireshark stable releases PPA maintained by the Wireshark Project (including me:-)).