When I was in Rome, the Vatican Cathedral of Peter and Paul (after the example of which Isaac was built) struck me not so much as the power of St. Isaac's Cathedral. Truly, it should have been made the main cathedral of Parvoslavia.
For me, the Kremlin entered the top disappointing sights. A couple of churches and a wall. Yes, historically beautiful, but interesting. But you expect more from the main attraction of Moscow.