Unity is the default desktop manager in Ubuntu since the 11.04 version (April of 2011) and this, for someone, is again today a problem.
Personally I think Unity is easy to use and I like it but I understand that other people prefer have a classic menu with applications collected in categories. maybe for habit with old versions of Gnome or Windows (like Windows XP or Windows 7).
But we know that the opensource world offers lots of alternatives. Nobody wants to impose a filosophy to any other. Everybody can cut their Linux based on own preferences.
The first alternative is to install another desktop manager instead of Unity, like Gnome, KDE, LXDE, Mate, XFCE, …
But if you like Unity and you want only restore the classic menu of the applications you can install the classicmenu-indicator package.
This package add a small indicator in the notification bar of Ubuntu. Clicking on it you can use the classic menu of the applications like in the following picture:
You can find this package in the Ubuntu’s repositories, so you can install it from Ubuntu Software Center or by the following command:
sudo apt-get install classicmenu-indicator
After the installation, the first time, you have to start it manually, searching it in the Dash of Unity.
Easy and useful, isn’t it?