Semi-obscure. I enjoyed the first few, but thought it got a bit weak towards the end. Speaking of which, Harry Harrison now has the dubious honor or writing what is rapidly being considered the worst alternate history series of all time: the "Stars and Stripes" trilogy, in which the USA and CSA put aside their differences in the middle of the Civil War to attack Great Britain, and by the end of the series have successfully(!) invaded the United Kingdom, to the applause of cheering crowds of the oppressed citizens of the UK.
Oh, and they casually invent the internal combustion engine and the tank just to make it easier. In the 1860's.