From the bibliographical standpoint, the publication of this work is rather unusual for a journal article. There are three different issues—the journal publication, the true offprint from the journal (extremely rare), and a commercially published offprint or separate edition. This separate edition went through several reprintings which are easily confused with the first printing. See Hook & Norman, The Haskell F. Norman Library of Science and Medicine (1991) nos. 695 & 696.
A summary of the different aspects of the theory linked to more details on different aspects follows:
"General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the state-of-the art description of gravity in modern physics. It unifies special relativity and Newton's law of universal gravitation, and describes gravity as a property of the geometry of space and time, or spacetime. In particular, the curvature of spacetime is directly related to the four-momentum (mass-energy and linear momentum) of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of partial differential equations.
"The predictions of general relativity differ significantly from those of classical physics, especially concerning the passage of time, the geometry of space, the motion of bodies in free fall, and the propagation of light. Examples of such differences include gravitational time dilation, the gravitational redshift of light, and the gravitational time delay. General relativity's predictions have been confirmed in all observations and experiments to date. Although general relativity is not the only relativistic theory of gravity, it is the simplest theory that is consistent with experimental data. However, unanswered questions remain, the most fundamental being how general relativity can be reconciled with the laws of quantum physics to produce a complete and self-consistent theory of quantum gravity.
"Einstein's theory has important astrophysical applications. It points towards the existence of black holes—regions of space in which space and time are distorted in such a way that nothing, not even light, can escape—as an end-state for massive stars. There is evidence that such stellar black holes as well as more massive varieties of black hole are responsible for the intense radiation emitted by certain types of astronomical objects such as active galactic nuclei or microquasars. The bending of light by gravity can lead to the phenomenon of gravitational lensing, where multiple images of the same distant astronomical object are visible in the sky. General relativity also predicts the existence of gravitational waves, which have since been measured indirectly; a direct measurement is the aim of projects such as LIGO. In addition, general relativity is the basis of current cosmological models of an expanding universe" (Wikipedia article on General Relativity, accessed 12-22-2008).