The low-dimensional electron systems that reside in artificial semiconductor heterostructures of great perfection are a contemporary materials base for explorations of collective phenomena and quantum phase transitions.  Studies of low-lying elementary excitations by inelastic light scattering offer insights on properties such energetic, interactions and spin magnetization.  We review here recent light scattering results obtained from two-dimensional (2D) quantum fluids in semiconductor heterostructures under extreme conditions of low temperature and large magnetic field, where the quantum Hall phases are archetypes of novel behaviors.  We also consider recent light scattering experiments that have probed the excitation spectra of few-electron states in semiconductor quantum dots.