Big but not all that imposing.
Beyond the square is the old KGB building, now renamed but employing teh same people doing similar things. On the roof is a heliport that used to be used to ferry prisoners to Siberia. Russian joke: What is the tallest building in Moscow? The KGB building - you you go to the roof you can see Siberia.
BTW: Red Square was named in the 17th century. It has nothing to do with red but relates to a Russian word meaning beautiful.