  We study the differential decay rate for the rare $\Lambda_b \to \Lambda (\to
N \pi)\ell^+\ell^-$ transition, including a determination of the complete
angular distribution, assuming unpolarized $\Lambda_b$ baryons. On the basis of
a properly chosen parametrization of the various helicity amplitudes, we
provide expressions for the angular observables within the Standard Model and a
subset of new physics models with chirality-flipped operators. Hadronic effects
at low recoil are estimated by combining information from lattice QCD with
(improved) form-factor relations in Heavy Quark Effective Theory. Our estimates
for large hadronic recoil -- at this stage -- are still rather uncertain
because the baryonic input functions are not so well known, and
non-factorizable spectator effects have not been worked out systematically so
far. Still, our phenomenological analysis of decay asymmetries and angular
observables for $\Lambda_b \to \Lambda (\to N \pi)\ell^+\ell^-$ reveals that
this decay mode can provide new and complementary constraints on the Wilson
coefficients in radiative and semileptonic $b \to s$ transitions compared to
the corresponding mesonic modes.
