Given the stunning, world-changing contributions to world culture that are connected to the Agora (philosophy, democracy, religion, public administration, and so on), the site was a disappointment, particularly when compared with the Parthenon.
Essentially, it's a ramshackle collection of uncared-for remains, presented without any sense of story, and without any real attempt at curation.
With a bit of thought and imagination, great things could be done with the Agora. It's disappointing that so little has been done.
I'm giving the Agora three stars because it's so historically important, and because it contains the lovely Temple of Hephaestus. Just expect to be disappointed by the rest of it.