Just very shortly:
A cabin with a window means that the window looks at the side of a tender boat just half a meter away. It totally blocks all view, the cabin practically equals an inside cabin. We were given a shady explanation on some sort of a "lottery" for guaranteed cabins, which means that Costa can give you worse cabins you thought you had paid for. Quite interesting practice from consumer protection point of view. So avoid guaranteed cabins and cabins on Deck 4.
Otherwise the cabin was clean, well maintained.