Gorilla Kingdom is certainly not realistic in the same way as Disney or Bronx in the USA. However, imo, it is no worse than, and in some cases it is better than, a number of the other modern Gorilla exhibits to be seen in other major European Zoos.
This photo was taken in March with short frosted- looking grass- during the summer months it is a lot lusher looking than this. When it first opened it was indeed very bare and empty looking but has improved a lot. More live shade trees and other vegetation e.g. bamboo clumps, would be the final improvement I would like to see. Maybe change the awful artificial tree too.