  Afterglows of gamma-ray bursts often show flares, plateaus, and sudden
intensity drops: these temporal features are difficult to explain as coming
from the forward shock. We calculate radiative properties of early GRB
afterglows with the dominant contribution from the reverse shock (RS)
propagating in an ultra-relativistic (pulsar-like) wind produced by the
long-lasting central engine. RS emission occurs in the fast cooling regime --
this ensures high radiative efficiency and allows fast intensity variations. We
demonstrate that: (i) mild wind power, of the order of $\sim 10^{46}$ erg
s$^{-1}$, can reproduce the afterglows' plateau phase; (ii) termination of the
wind can produce sudden steep decays; (iii) mild variations in the wind
luminosity can produce short-duration afterglow flares.
