I came across Camus’ Caligula while doing my MA at the University. It was part of the syllabus in a paper titled Historical Drama.
The book deals with the tyranny of Caligula, analyzed from the perspective of Camus. His preoccupations with existentialism and Marxism have influenced this book to a great extent. Historical plays are usually plagued by a desperate attempt by the author to be realistic & truthful. This is common with writers who have low imaginative faculty and even lesser insight. It goes without saying that nobody reads a historical play for an accurate account of truth, and any anachronism and digressions from truth would be accepted, provided there is a genuine reason for the author to have done so. So one should not read Caligula to learn about the reign of Caligula, the emperor; but one may read it if one is interested in the philosophical ponderings of a great soul; dealing with sublime questions of life, power, tyranny, love, etc.
Camus’ style is a bit difficult, especially for people who are not familiar with methods of expression adopted by philosophers. It would be advisable that a reader gets acqauinted with the concept of existentialism before he ventures into Caligula. A similar book is Tughlaq by Girish Karnad. Karnad is more simple, straightforward, realistic, and truthful than Camus. However, he too deals with the questions of power, existence, life, etc. in Tughlaq.
I am not much familiar with other writings by Camus.