There are no written reviews. The “details” is merely a breakdown of how many people gave this many number of stars and how many people gave it that many number of stars.
There is a Wishlist topic for written reviews:
If this is something important to you, please feel free to vote for it.
Note that there is no way to see who voted in these and how many stars individual people gave.
Your only option when leaving a review is to give it a number of stars. First, you must navigate to the Marketplace item that you purchased. When you move your cursor over the stars, you will see them highlighted.
When you click on a Marketplace entry, the last rating you gave it will be shown. The number of stars you gave it will be highlighted.