I am playing with the diplo mod at start and then disabled(i spend hours putting all the civs at their correct location in ige).
Loss of science and the death of a great thinker happens very often, i´m in classic and had no GP other than prophets and generals and a single ingenieur.
There are some citybuildings in late ancient wich lack proper explanation, they have strange religious symbols, one comes with Elite.
There are not enough religions for every nation.
Edit: The city buildings seem to be the unique religios ones. I can build all of them, wich shouldnt be the case.