The Visitors has many of the trusted Simak elements-- otherworldly intelligence, a focus on small characters and places, and a folksy kind of diction and tone. Unfortunately, it lacks the focus and clarity that makes books like Way Station and Project Pope such striking books to read.
Still, there are many interesting elements that make The Visitors worth the time to read. Despite the lack of unity, it contains some of Simak's most interesting observations about religion and economics.
If you have not read Simak before, begin with Way Station or Enchanted Pilgrimage. If you are a Simak fan, it is most certainly worth the time to read despite not being his best work.