A theoretical model for the investigation of the dynamics of microcavity polaritons in the strong-coupling regime is proposed. The resulting photoluminescence dynamics at small angles is studied as a function of the angle of observation, the cavity detuning, the lattice, and the free-carrier temperature. For small detunings, the strong dispersion of the microcavity polaritons at small angles results in a bottleneck relaxation dynamics, similar to the bulk one. However, important differences, related to the reduced dimensionality of the system, are found. In particular, a larger emission from the upper polariton with respect to the lower polariton is found for any temperature. Moreover, a two-lobe angular emission from the lower branch is also expected. In the case of large pump excess energies, when hot carriers are injected into the system, longitudinal-optical-phonon emission has also been considered as a possible polariton formation mechanism, and shown to reduce only partially the effects summarized above.