LAAS approaches (GLS as boeing calls them) do not depend on barometric altimetry anymore and can achieve up to CAT IIIb precision. However that is still in development and only CAT I is approved so far. WAAS is CAT I equivalent currently in some parts of the world and Baro VNAV limits other operations to NPA values.
Flying GLS approaches is basicly the same as any ILS, however the approach path can be curved and support different descent angles in one approach. In practical flying it is very very smooth indeed and allows autolands allready (at least in 737s, delivered with GLS standard autoflight system).