My wife and I stayed here in early October and were very happy with our choice of the apartment. It's on the 4th floor (5th floor american style) with an elevator. The compact apartment was very clean and neat, with the beautiful view of the Opera. The bedroom is in a 5' high loft and the shower is not large - a tall or heavy person might not be comfortable here.
The building does have a beautiful marble staircase, but you'll see some peeling paint in the common areas before you reach the newly decorated unit. The building is across the street from the Corvesy parking garage, which has 1 hour free parking - convenient if you want to drop off luggage before returning your rental car. It's centrally located - a short walk to the shops of Old Town, the fountains on the Promenade du Paillon and the Riviera and only a short bus ride to nearby Eze (definitely worth seeing).
The owner was very accommodating - he waited for us an hour past when we should have arrived (traffic delay us - I sincerely recommend you ditch your car if you're staying in Old Town Nice), explained everything we needed to know about the unit and met us at our convenience to retrieve the key before we departed.
We're happy we stayed here!