Answer by Marc Srour, Invertebrate palaeontologist, arthropod systematist, historian of biology
Darwin's theory is not the end of evolutionary biology. That's like saying Newton developing calculus was the end-point of mathematics. If we still ran strictly by Darwin's conception of evolution, biology would be pretty different, and far less fruitful, than it is today.
What do evolutionary biologists do? Many, many things. Some of us investigate the history of life on Earth, using the fossil record to tell us how macroevolution takes place, giving us information about our evolutionary ancestry. Others concentrate on genetics to investigate how new species form, or to give an alternative perspective on the facts we get from the fossil record. Others combine evolution with other fields, like developmental biology or biogeography, to provide more depth and insight to our knowledge of the history and diversity of life on Earth. Others apply evolutionary principles to agriculture, to medicine, and to society to give us practical, tangible benefits, e.g. in helping to fight pests or finding new drugs and ways to fight disease, and to figure out better ways to structure society.
In other words, evolution has grown far beyond Darwin. There are evolutionary biologists who spend their days working with fruit flies; others with embryos; others go out into the field; others do everything just with a computer. A lot of evolutionary biology is "blue skies" research, with no, or little, direct applied value. Some of it is done with a practical purpose in mind.
All of these disparate researches come together to give us a framework within which we can understand how life works. Evolutionary biology can be considered as an apartment building in which all the other fields of biology are housed.
There are plenty of things left to discover. Sure, at the surface, everything looks nice and solved, but once you dig deeper, controversies and fights start to emerge. For example, even something as basic as how two new species can form in a particular scenario can get two evolutionary biologists arguing fervently, precisely because not everything is solved.