The setting: the two countries of Anatoray and Disith are engaged in an endless war, governed by strict rules enforced by the Guild. Most of the battles are fought with flying vessels, armed not only with batteries of cannons, but also with rifle infantry (yes, people on ships, shooting at each other in the sky). A postal service via small, fast flying machines connects the various parts of each country. Communications between the countries are nearly impossible: the Grand Stream stands between them, a large region of constant turbulence. The two Anatoray protagonists, Claus and Lavie, are orphans, their fathers having died years before, trying to cross the Stream to deliver a peace proposal to Disith. Now, they're charged with delivering young Alvis to the mysterious ship Silvana, and the Guild does not seems completely pleased about that.
It's not a totally original story, but it does not matter much: the characters are interesting, their interplay is well written, and most of the plot is tight enough to let you ignore the occasional issue. I think the last episode makes a bit of a hash of things, skipping a few explanatory scenes that would have much helped to understand what's going on, but if you watch it a couple of times you should get the gist. Mind you, I also don't like the ending, so my opinion may be a bit biased.
There's echoes of Miyazaky's Nausicaä in the set-up of the war, and of Matsumoto's Harlock in the crew of the Silvana; in Fractale (8 years more recent than Last Exile) you can see that the power dynamic between the Temple and Lost Millennium is very similar to the one between the Guild and the Silvana.
The society, technology and the aesthetic are the now familiar anachronistic mix of steampunk: Victorian-era military uniforms, stylised military rules and honour-bound officers, brass and leather and goggles everywhere, machines running on steam and non-obvious tech (here, mostly anti-gravity). The main exception is the Guild, with much more advanced technology and completely different aesthetic, but that only serves to mark them as different and to support their "right to rule".
An interesting detail: the title of each episodes references an aspect of the game of chess, relevant to the plot of the episode itself. Given how the Guild is playing the two countries against each other, and the complicated and strict rules under which the war is fought, this choice is not just a quirk.
