Perhaps the lofty rating set my hopes too high. The idea behind the Light Ages is certainly interesting: instead of James Watt discovering steam engines, Ian MacLeod in Light Ages creates an alternate history England where "aether" is discovered. The properties of this magical substance allow humans to build structures, devices, creatures that would otherwise be impossible. For example, the aether allows the construction of fantastic towers that would otherwise crumple under the force of gravity. Aether allows unicorns and dragons. The secret for using aether requires spells that are painted on during the objections construction - the secret of these spells is closely guarded by the guilds that control them. There are Toolmaker Guilds, Telegraph Guilds, etc.
But using aether has unfortunate consequences. Aether use creates "engine ice", which pollutes the landscape. Exposure to aether can warp a person - they become trolls or changlings, feared and tormented by the untainted humans. Another unfortunate aspect of the aether is that it must be mined from deep under the earth at the English town of Bracebridge, and the supply could run out [I must have missed the explanation in the novel - if the aether supply is running out, then what alternate source is used to keep the English economy going?]
MacLeod paints a complete alternate society based on aether. Our hero, Robert Borrows, gets a tour of all aspects, from the London slums to the highest of high society. Robert is motivated to be a revolutionary, aether has corrupted his beloved mom, and now he wants to tear down the society that benefits from the misery of others. All of this is well portrayed and imaginatively described, so why the big disappointment? I think it is the lack of conflict in the novel. Our hero, Borrows the revolutionary, never is placed in any apparent danger, despite the fact he wishes to bring down the civil order. No secret police, no jails, no fiery passionate speeches on the soapbox in the public square. We are told Borrows writes for a revolutionary newspaper, but we are not told what he writes. When he meets the cream of the social order, at the pinnacle of society, they are not in the least concerned by his revolutionary ideas, indeed they seem eager to befriend him and aid in the destruction of this Age of Aether. The lack of conflict results in a languidly paced novel, a tour through a well constructed alternate England. This is still a much better novel than MacLeod's earlier effort, The Great Wheel, which is a real snoozer. The Light Ages is a fine read, but don't expect heart pounding action.