In the opinion of many AVIDS, this was the best of the three MYST books released so far. While I thought it was good, it was not, in the opinion of this particular AVID, the best.
MYST: The Book of Ti'ana (1996) went further into the back-ground story of MRED. It explained the story of Ti'ana in great detail; how she came to find D'ni, and the fall of the D'ni. It had many tidbits in it about the D'ni civillization, and certainly whetted the appetite of many AVIDS for all things D'ni, once again.
While this also was not my favorite, it certainly came very close.
MYST: The Book of D'ni (1997) told us what happenned to our friend, Atrus, between Riven and ExilE. (ExilE wasn't created at that time, but it happens after BoD) Atrus, Catharine, and a few friends from some ages tried to restore D'ni to it's former glory--only to discover some dark secrets of the past...
In my humble oppinion, this was, by far the best MYST book in the series. I really enjoyed seeing what became of Atrus and his family and the rest of the D'ni culture.