Well, you can look up its reviews. Basically, it was hastily written, tendentious, and superficial.
It’s popular because it (falsely) promises an efficient survey of a discipline most people think is important (although not important enough to devote much study to in a rigorous academic program). So people outside of philosophy think, “Aha, this will make short work of what’s ordinarily a year’s worth of courses!” But it does no such thing; even Russell himself expressed some misgivings about the work.
Really, the best way to become acquainted with philosophy is to read primary sources. It could be the ancients, Descartes and his successors, or twentieth-century. But anything that purports to provide a one-author, concise history of Western Philosophy from Parmenides to Putnam is pulling your leg.
Hegel got conservative in his later years, yes, but by no means pro-monarchist. Throughout the Napoleonic Wars he was a firm supporter of Napoleon, since Hegel saw in him the agent through which philosophy was acting to change European society (namely, getting rid of the old order and putting the bourgeoisie in power - something the bourgeoisie themselves were unwilling to do).
While this was never completely done (nor would it have been even if Napoleon had ultimately won after 1812) Napoleon’s conquest of Europe forced the monarchies to make radical changes (the Prussian monarch had to promise a constitution in order to get enough citizens interested in fighting Napoleon, for instance). Hegel, however, still thought Prussia had a long way to go in order to come close to matching his vision of a constitutional monarchy.
Nevertheless, in the last decade of his life Hegel was certain that history had pretty much come to an end, and no further changes were really about to happen. He opposed the revolutions of 1830 because he was convinced that philosophy, being the motor of social change, could no longer imbue the age with the urge for change. But it’s important to remember that he wasn’t defending the order he once used to attack; he was defending the changes in the order that had come about as a result of Napoleon’s conquest.