The establishment of a definitive cosmological picture has been one of the triumphs of 20th Century physics. From Einstein's first investigations into relativistic cosmological models, through Hubble's discovery of the cosmic expansion, to the discovery of the Cosmic Microwave Background Radiation in 1965, most physicists would now agree on the basic ingredients of what might as well be called "the Standard Cosmological Model". The astrophysics of the 21st century will consist largely of filling in and understanding the details of this model: a nontrivial process that will consume substantial human, technical and financial resources.
While there are suggestions that the standard model may not be complete, the data as a whole do not as yet demand any further parametrization such as "quintessence". Of course, as our understanding of fundamental physics deepens, the standard model might be recast in a new wider, more profound, framework such as that offered by brane cosmologies.