  We start with a rather detailed, general discussion of recent results of the
replica approach to statistical mechanics of a single classical particle placed
in a random $N (\gg 1)$-dimensional Gaussian landscape and confined by a
spherically symmetric potential suitably growing at infinity. Then we employ
random matrix methods to calculate the density of stationary points, as well as
minima, of the associated energy surface. This is used to show that for a
generic smooth, concave confining potentials the condition of the
zero-temperature replica symmetry breaking coincides with one signalling that
{\it both} mean total number of stationary points in the energy landscape, {\it
and} the mean number of minima are exponential in $N$. For such systems the
(annealed) complexity of minima vanishes cubically when approaching the
critical confinement, whereas the cumulative annealed complexity vanishes
quadratically. Different behaviour reported in our earlier short communication
[Y.V. Fyodorov et al., {\it JETP Lett.} {\bf 85}, 261, (2007)] was due to
non-analyticity of the hard-wall confinement potential. Finally, for the
simplest case of parabolic confinement we investigate how the complexity
depends on the index of stationary points. In particular, we show that in the
vicinity of critical confinement the saddle-points with a positive annealed
complexity must be close to minima, as they must have a vanishing {\it
fraction} of negative eigenvalues in the Hessian.
