Audacious is a music player that is popular on Linux. It is based on XMMS, but has a simple GUI and operation that is straightforward.
This simplicity is something that is lost in most modern music players, like Rhythmbox or Banshee. They try to be the next iTunes. The UI is too complicated, they cannot simply open some files and play them. They want to manage your audio files for you and so on.
Installing Audacious is easy:
$ sudo apt-get install audacious
The only real feature I am missing in Audacious is the ability to delete files from the filesystem. That feature can be obtained by installing a more recent version of Audacious, as described here.
Tried with: Audacious 3.4.3 and Ubuntu 14.04