Right off the bat I'll make a disclaimer. Obviously the game from which these books are derived, All Quiet on the Martian Front, is a direct competitor to both HQC and Space 1889 filling basically the same niche. The AQotMF setting is a limited scope universe dealing only with action during a second Martian invasion in 1909 on Earth. The novels give a small window into Martian activities on their dying homeworld, but the action centers on Earth and in the Novels in the American Southwest and Washington D.C.
Now disclaimer aside Scott Washburn has produced two really excellent novels. He does character and action very well and AQotMF has provided a strong detailed setting. The point of view characters, including a young female from a ranch in the territory first struck by the Martians, a grizzled old Cavalry Sergeant and a newly minted Ordnance Officer (as well as occasional glimpses of President Roosevelt and his General Leonard Wood) give a wide range of perspective on the war and allow a view both from the front lines as well as in the proving grounds, laboratories and finally into the strategic conduct of the war. Often such a group of main characters would see stilted and forced but the narrative flows naturally from one location or theater to the next.
In addition to the main characters the writer weaves in a number of historical figures. Many of these will be well known to fans of the period or of steampunk: Tesla, Patton, MacArthur, Goddard, Edison and many others all make appearances as do a number of lesser known persons. In terms of research Washburn has done an excellent job discovering men and women who would have been involved in various ways and having them walk onto this stage.
He also has done a good job with industrial and logistical, issues. Baldwin Locomotive is building steamtanks and Cramp of Philadelphia is brought into a consortium to build larger land ironclads.
There is also a Martian Point of View character. This addition to the cast gives the reader additional insight into the martians, their abilities, weakness and goals. In some ways I like the original Wells treatment of the Martians, where the reader sees only their actions through human eyes.
There are some strange errors though, which few people would catch but did stand out to me. First the United States Army is armed with French M1897 75mm field guns at the start of the war. This may a result of rearmament in the aftermath of the Martian Invasion, otherwise the Army was armed with 3 inch weapons of domestic manufacture. Also odd is Washburn's discussion of 10 inch seacoast mortars. It is true that the US Coast Artillery Corps did use seacoast mortars in large numbers. Its also true that a 10 inch mortar was designed and at least one and possibly two prototypes were built. However all the rest of the mortars, produced in a number of models, were in 12 inch caliber. It just seems strange that Washburn changed the size of these weapons, or that an error like this crept in. These are really small nits and for only a tiny minority of readers would it even be noticeable.
Interesting omissions include railway artillery and armored trains. The latter is mentioned as being developed in a meeting described late in Breakthrough but although railways are critical elements of the story the Americans never use them directly for combat, only for transportation. This is also strange since the United States had experience with both railway guns and armored trains dating back to the American Civil War.
OK those are basically quibbles. Even with those really minor errors these are strong books. They are good stories told well. If you have any interest in Steampunk/VSF (or in this case Edwardian Science Fiction) these are well worth reading.