This paper presents an analysis of the fundamental role of nonplanar orientation on the complex rheological behavior of uniaxial rodlike nematic fluids. Evidence of flow-induced nonplanar orientation is captured by three-dimensional nonuniform orientation simulations, using the Leslie-Ericksen equations, and by scientific visualization. Unique and direct correlations between rheological material functions and the underlying nonplanar microstructure are identified and characterized. The first direct semiquantitative rheological comparisons between simulations and actual experiments, for a series of representative shear flow histories at moderate Ericksen numbers, are given. Very good agreement is found between the theoretical predictions and experimental measurements for start-up, reversal, and cessation of isothermal, shear flows.