Relying on HSE03, G(0)W(0), and random phase approximation + G(0)W(0) approaches, this study provides a complete characterization of the electronic properties of six ZnO bulk polymorphs, including quasiparticle spectra, absorption, and electron energy-loss spectra. It focuses on the series zinc blende, wurtzite, body-centered tetragonal, sodalite, and cubane structures, along which atoms have similar local tetrahedral environments and decreasing atomic density, to which the hexagonal boron nitride structure was added. All trends in the electronic properties-gap opening, blueshift of low-energy interband transitions, redshift of the main absorption peak, the frequency at which the real part of the dielectric tensor vanishes, and the plasmon energy-were interpreted in terms of the two main effects resulting from the decrease of the atomic density along the series: a bandwidth narrowing close to the gap edge and a decrease (in absolute value) of the electrostatic potential acting on the zinc and oxygen ions. This work gives firm grounds to help and foster spectroscopic experiments on ZnO polymorphs. It represents a preliminary step towards the study of thin-film properties.