I was actually thinking about this in the TL-191 threads: 1. Harry Turtledove's writing gets knocked around (that Custer scene!) but the TL's implicit premise is indeed interesting--"what would America look like if it wasn't 'America'?" you have a North with centralization, revanchist militarism, snitches and stoolies instead of celluloid cowboys, a draftee mega-Army in Feldgrau and Stahlhelme, metric and Celsius, heavens-knows-what Prussian ideologies, barbed-wire camps, and willing to go all the way to kick the Sioux and Apache outside the borders (if they're lucky), and a South repeating (all too closely) the path of 1918-45 Germany; so he takes thinks that are actually inherent in US history and juices them up, implicitly making the reader think "so ... what is 'American'? if our sins and ills are inevitably written in stone since 1619--why didn't OTL turn out the same way?"
1b. on edit: High Castle tries to do this, but ultimately just blows up Lady Liberty and the Bell and slaps Hitler Youth and SS uniforms on everyone, it's too much of an imposition
2. SM Stirling's Draka series even more intentionally creates a complete "anti-USA": Revolutionary-War Loyalists hook up with Boerarchists and Confederado slavelords; this TL is more on-the-nose than Turt, but doesn't really cross-examine "Americanness" except create a conveniently-foreign OPFOR (that AmericaTM teams up with the Nazis to fight)
3. and I've had contrary thoughts about Philip Pullman's "His Dark Materials": this TL's supposed to be a Catho-Calvinist theocracy that hauls off freethinkers, jails kings, and sows fanatical hashishin across Europe: it's so oppressive the nominal Bolivar-style liberator can only free his home TL by slaying Jehovah/the Demiurge himself: but Lyra's world also has witches (real witches) that are shocked at the idea of mass persecution, no Shoah, no World Wars, and an industrial base that can *build a Nuke, target it by quantum entanglement across the multiverse, and eventually nuke Hell itself*: one of my notes for this world is "our TL is the one that looks dystopian to other TLs"