This is a comparative study of the adsorption dynamics of increasingly longer polyatomic molecules on a planar surface. We perform kinetic Monte Carlo simulations of the gas uptake to identify the molecular mechanisms and parameters that govern the evolution of the adsorbed film to its final equilibrium state. We also develop an analytical model for the adsorption dynamics of mono-atomic gases that demonstrates a direct correlation between the strength of the gas-gas interaction and the adsorption rate dependence with coverage. When this is added to the effect of the orientational freedom of polyatomic molecules, we are able to explain the change in the adsorption rate dependence observed experimentally for longer molecules.