We stayed at the Carlos V for 2 nights. Our room was a good size with brightly colored walls and paintings. The bathroom was large and newly redone. As someone else mentioned in her review, the walls are thin. We had a screaming child next door, but this could have happened anywhere. Our main reservation about the hotel was the indifference of the staff. They weren't unhelpful but gave minimal information. An example - The hotel desk gave us directions to the garage to park our car (which was in the same building as the hotel, but in essence you have to go around several blocks to get back to it). When we got there, a sign said "completo" and there was a cone in the entrance. So we went around the block(s) again. Same story. So we parked in front of the hotel and went up to the 4th floor of the building (where the hotel is), and the receptionist said, "Well, did you honk?" Then she called the garage and asked if there was a space for us. There was. So we went around again, honked, and the attendant came to the entrance to let us in. This is just one example of giving minimal info. There were others.
The location of the hotel is good as was the price. The hotel is not far from many of the tourist sights. We walked uphill to the Alhambra. It took about 1/2 hour. There's a grocery store on the ground floor of the building. And it's close to many restaurants and tapas bars.
Although we would give the hotel some plusses, I don't think we'd stay at Carlos V again. We prefer a hotel with a more welcoming staff. But it was a good value for the price.