  A decade ago brief summary of the field could be formulated as a discovery of
strongly-coupled Quark-Gluon-Plasma, sQGP, making a very good liquid with
surprisingly small viscosity. Since 2010 we have LHC program, which added a lot
to our understanding, and now there seems to be a need to consolidate what we
learned and formulate a list of issues to be studied next. Hydrodynamical
perturbations, leading to higher harmonics of angular correlations, are
identified as long-lived sound waves. Recently studied reactions involving
sounds include phonon decays into two ("loop viscosity"), phonon+magnetic field
into photons/dileptons (sono-magneto-luminescence), and two phonons into a
gravity wave, a penetrating probe of the Big Bang. The mainstream issues in the
field now include a quest to study transition between $pp,pA$ and heavy ion
$AA$ collisions, with an aim to locate "the smallest drops" of the sQGP
displaying collective/hydrodynamics behavior. The issues related to
out-of-equilibrium stage of the collisions, and mechanisms of the
equilibration, in weak and strong coupling, are also hotly debated.
