  We consider the energy-critical non-linear focusing wave equation in
dimension N=3,4,5. An explicit stationnary solution, $W$, of this equation is
known. The energy E(W,0) has been shown by C. Kenig and F. Merle to be a
threshold for the dynamical behavior of solutions of the equation. In the
present article we study the dynamics at the critical level E(u_0,u_1)=E(W,0)
and classify the corresponding solutions. We show in particular the existence
of two special solutions, connecting different behaviors for negative and
positive times. Our results are analoguous to our previous work on radial
Schr\"odinger equation, but without any radial assumption on the data. We also
refine the understanding of the dynamical behavior of the special solutions.
