We have investigated the structural, electronic, and optical properties of partially strain-relaxed InxGa1-xAs layers, grown by molecular beam epitaxy on both misoriented and nominally flat (001) GaAs substrates. We find large anisotropies in bulk strain relaxation, interfacial misfit dislocation density, dark-line defect density, and electron mobility, as well as a polarization anisotropy in cathodoluminescence for epilayers grown on misoriented substrates, in comparison with those grown on flat substrates.