Finished Ruled Britannica. Everything that bothered me about this book would prevent me from reading Turtledove's other fiction, at least those bits based in history other than the periods I'm interested in. Basically, his adherence to history can be cumbersome: it was difficult to get into the dialogue because it was "Elizabethan-y," and there was an awful lot of detail that did jack for the plot as a whole. This could easily have been a much shorter, much tighter book, and would have been better for it.
That said, he did a great job writing an alternate history without unnecessarily bending the historical figures to it. This did cause problems when his homage turned to pastiche (I'm looking at you, Womanizer Lope and Coward Shakespeare and Carouser Kit). Luckily, he wrote characters that were entertaining to follow nonetheless.
Started Red Mars. Only a few pages in, but I'm already liking it. Excellent!