Being fond of ancient Sumer in general and the Gilgamesh epic in particular, I found Mr. Silverberg's book a profound disappointment. It appears that the author's intention was to rework the venerable story to remove its fantastic elements. Along the way he practically ignores an interesting milieu, makes the characters boring, and replaces dynamic episodes with confusing ones.
Admittedly, Mr. Silverberg did make an effort to make his characters seem as though they actually are living in a different day and time. However, as historical fiction this book falls flat. (If you want historical fiction set in Sumer check out The Three Brothers of Ur by J.G. Fyson, and forget this book.)