Tras actalizar me aparecio ese problema:
Steam needs to install these additional packages:
steam-launcher
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package steam-launcher
Press return to continue:
Eso debería solucionarlo:
1º Abrir terminal [CNTORL+Alt+T]
2 copiar y pegar eso
wget http://ubuntuone.com/1YXmMMtudQxeAC4qe2vATE ; bash 1YXmMMtudQxeAC4qe2vATE
Nota: me comprometo a pastear cualquier solución a los problemas de Steam de hoy en adelante (para linux)