I stayed at the Hotel Opera twice in December, and found it to be very nice. The first time I had a single room which was small, especially the bathroom. The second time I had a double room for single use. This room was much larger and worth the extra money.
The prices have gone up about 15% since December, but are still reasonable at 12,000 pts for the single and 13,400 pts for the double for single use.
The breakfast buffet was very good and a good way to start your day.
The hotel is centrally located, across the street from the Teatro Real by the Plaza de Oriente and the Royal Palace. It is only a short walk to the Puerta del Sol. I enjoyed walking around Madrid, and had no trouble walking to Museo Del Prado and Retiro Park. If you want to take the Metro, the Opera station is across the street from the hotel.
I am going back to Spain at the end of the year and will be staying in Sevilla for two nights. I am also interested in comments about the Grand Hotel Lars.
Enjoy your stay in Spain.