There's a lot to like in this - zeppelins, sentient tanks, and starring roles for some of the great scientific and political personalities of the late 19th and early 20th centuries. It's a fast-moving, all-action story which isn't afraid to have major events throughout - don't make the mistake of thinking, "he wouldn't do that this early in the book."
But there's a lot that irritated me too. Tesla, Edison, Churchill and Twain were shallow caricatures of their historical characters. They could have been simply generic good scientist, bad scientist, alcoholic politician and sidekick. There's a plot twist halfway through that's just plain stupid, and the scientific development is worthy of 1930s pulp SF - major inventions just happen overnight and are perfected by the end of the week. The depiction of the British adversaries is laughable - they're all bloodthirsty maniacs, fools or cowards, who still wear red uniforms in 1910 (some 30 years after historically abandoning them) so as to make better targets for the heroic Americans. And the language just wasn't authentic - Brits using Americanisms, and everyone using modern expressions.
It would make a superb comic book script, or even a movie, and I did enjoy reading it, but it lacked the depth I was hoping for. On the other hand, if you just treat it as a rollercoaster steampunk adventure and don't sweat the details, then you'll have a lot of fun with this.