The trilogy is essential, but since Asimov also capitalized on his own genius by writing what seems to be hundreds of lesser Foundation stories, it can all get very confusing and a bit draining. This is the second book in the original trilogy, so it is from a science fiction point of view essential reading. The trilogy itself comes up with two highly memorable characters, Hari Seldon, the psycho-historian, who uses Mathematics to predict the future and establish a "Foundation" that will limit the dark ages after the fall of the "Empire" to a single millenium (as opposed to ten.) He reappears as a hologram at certain points in the story with more or less accurate takes on what is happening in "History" at that point.
The other very memorable character is the Mule. He represents the variable that makes predicting "History" mathematically a tricky business at least, not to mention impossible. He is a nasty totalitarian character who strangely in Asimov's hands manages to elicit some sympathy. Asimov is playing with the idea of predicting human behavior scientifically (or controlling it scientifically,) but this character is also a humanistic meditation on how masses of people get overwhelmed by evil social forces like fascism and soviet communism. You can see that Asimov lived through the era of Hitler, Mussolini, Franco and Stalin and that these cult of personality tyrants and the submission of masses of people to their destructive and sadistic wills profoundly affected his view of human nature. Foundation and Empire seems to be an attempt to come to terms with that experience, and so has something to say about the specifics of twentieth century history, as well as about historical philosophy.