Interesting, at times fascinating, but also occasionally frustrating and annoying. Gellner posits three main stages of society: hunter/gatherer, agriculture and industry. He argues that the nature of cognition, production and coercion (power) is quite different in each stage. The development of an industrial society based on industry was a singular event, since agriculture, from which it arose, is inherently conservative and stable. Very particular circumstances had to occur simultaneously for a rational, enlightened, liberal society to emerge.
Some observations and analyses are convincing, others not quite. A major issue is the pervasive lack of concrete examples. For instance, Gellner discusses at length the "many-strandedness" of cognition in hunter/gatherer and agricultural society, and contrasts it with the "single-strandedness" characteristic of rational thought. But he gives few, if any, concrete examples of what this many-strandedness consist of.
As to the writing, it is clear and reasonably straightforward, but with an annoying habit of being indirect. Instead of being explicit that some argument or observation is about, say, the French Revolution, Gellner wraps it up in indirect descriptions, assuming that the reader can figure it out for himself. Elegant, perhaps. But also intellectually arrogant.