I bought S M Stirling's novel Conquistador, mainly because I loved his The Peshawar Lancers.
The premise is that an invalided soldier from WW2 accidentally creates a portal to a world in which Europeans never made it to the Western Hemisphere. He gathers a few of his former troops, and they secretly colonize the alternate California. There are factions among the colonists, and after a couple of generations, there's some plotting which might reveal the secret of the Portal. Our hero, a game warden, stumbles into this and gets embroiled in the infighting.
As I noted previously, the great thing about Peshawar Lancers was the flavor of his version of Victorian India--the feeling that there is a whole world going on around the character, with a richness of detail. Conquistador doesn't have the same amount of texture. Of course, part of that is because Conquistador largely takes place in a new world, so it's entirely justifiable. I should also point out that "not as much as Peshawar" means "not as much as one of my favorites." I've read a number of fantasy novels which were passable but felt like the history, geography and culture took less than a day to work out. Conquistador doesn't have that problem.
One problem that I did have with it was not its fault. Once I realized the situation was "a limited group of people can travel to another world, and their families control society", I felt some distaste for the book. I eventually realized that this was because the premise is very similar to Family Trade, which I'd read and disliked. If you've read the Stross book, don't let it taint Conquistador, which I found to be much better.