In the 2017 video game Middle-earth: Shadow of War, Minas Ithil/Morgul is depicted as a walled citadel with a sprawling city at its foot. How accurate is this when compared with Tolkien's writings?
First of all, the game is inspired by the movies more so than the books.
Regarding the city's size: neither Minas Ithil nor Minas Anor were big cities originally. The capital of Gondor was the large city Osgiliath located between them. When Osgiliath fell (far later than Minas Ithil), Minas Anor/Tirith became the new capital and probably grew quite a bit from there on - although it's not really clear how much of Minas Tirith that is Anarion's original design and how much that has been added later.
Given that the size of the city Minas Ithil isn't great in the game, I'd say the size is fairly accurate - and I would expect it to be smaller than Minas Tirith in the Third Age.
There's not a lot of detail describing the city in the books, other than that it is located in a mountainous valley. Quoting Tolkien Gateway (which in turn quotes The Two Towers, "The Stairs of Cirith Ungol"), it looked like this:
In its prime, Minas Ithil was a beautiful place. The moon cast silver light throughout the courtyards and streets, and reflected off the marble walls, so that it seemed to shine. The houses also shone white. The city also had one tall tower, with many windows, that rotated slowly. The city was accessed by a road, which was said to gleam like the city's white marble walls, running over a bridge as it crossed Imlad Morgul. Large meadows were placed on both banks of the stream.
This matches the game fairly well: they have the bridge, the white walls etc and they probably did at least a bit of research there.
The "seeing mini-towers" (I forgot what they were called) are however entirely made up by the game designers and don't exist in the books.
The big arena in the game is probably also made-up, as there's no mentioning of one in the books. Far later down the time line than the game, the last King of Gondor, Eärnur, does however supposedly die in a duel against the Witch-King, taking place in Minas Morgul. Or rather, the Witch-King challenged him to a duel, Eärnur rode to Minas Morgul and what happened to him isn't known. There could have been a duel in an arena like the one in the game, but that's just speculation (although it is highly unlikely that the Gondorians would build an arena for the purpose of gladiator games, more likely for sports or theatre etc).