Ackerman has written an extensive foreward in which he gives details of Stephens' background and the circumstances surrounding the trip described in this edition.
One of the first things that I noticed was that Stephens had made two trips to Mexico, the second trip occurring shortly after publishing the description of the first trip. The two different trips had distincly different itinararies. The first, the one Joseph Smith read and complimented was restricted to Guatamala and the second to the Yucatan. To my knowledge, Joseph Smith never commented on the second volumes that came out in 1843 although he may have been aware of their existence.
It is of interest that some proposals of book mormon geography confuse these two volumes and quote the second set as though it were that described by Joseph Smith. Most scholarly proposals for BofM geography limit the Nephite and Lamanite cultures described in the Book of Mormon as centered in Guatamala and Chiapas (the region described in Stephens first publictions) with little or no indication of any significant presence in the northern part of the Yucatan peninsula. A recent proposal discussed on this forum suggested that Tulum was a BoM city. First of all, Tulum was occupied well after the BofM period and second it was visited by Stephens only on his second trip. It is unlikely therefore that Tulum was settled by Nephites although it may have been settled by believing Lamanites after the final destruction of the Nephites.
As I continue to study Stephens work I will try to present some of my insights as to why joseph Smith might have been so enthused about Stephens descriptions and theories about the Mayans described in his first set of volumes.