I have GMed campaigns using both Xa-Ar and Emer III in the last years.
They are full architectural details of new and old civilizations that allow you to really paint a picture to the players on the different locations.
There are different types of adventures, in city and wilderness settings, with political plays, warzones, ruins to explore.
There are different races, cultural clashes, linguistic details, and also magic items of different levels.
There is enough content in both books that each allowed me to GM for 2 years, playing almost every week. And there are tons of references, dungeons, locations and quests that I did not get a chance to use; I could probably pull off another 2 year campaign by mixing them up.
Also, Emer III in particular is a pleasure to read, even if you currently don't have an active group to play with.