Cassa Massimo is one of the most wonderful places I could imagine. The flat is huge and spacious, provides a lot of common space. Equipped with everything you might need. Only down side - the TV has only Italian channels.
We were welcome with food - Sicilian specialties, wine, appetizers. It was great as we arrived late in the evening. Everything was clean and prepared for us. Next day (Sunday) we had some problems with figuring out how to turn on the gas but the hosts immediately came to help us. They have also provided very good information on what's worth seeing.
The flat is on the fist floor on a street that is filled with restaurants. This can be seen both as an advantage - you are in the middle of the night life, few meters away from Teatro Massimo - but can also be seen as a serious problem - one of the bedrooms has windows facing the street. If it is warm you will want to keep them open, but that will mean you feel like you're sleeping in a restaurant (mostly during the weekends, the rest of the week its calmer). I had no problems with that but my parents complained a bit. The other bedroom is very quiet.
There is a food market near by where you can find amazing and fresh seafood and vegetables. We found the restaurants pretty pricy and not so good, so most of the time we cooked at home. If you don't speak Italian make sure that they weight your groceries on the market - else they tend to over charge a bit. A few cents, maybe a euro, but it's annoying.
One thing we realized the last day - there is an "in-coop" next to Politeama. If you're looking for some kind of a bigger, Safeway type shop - that's your place. It is easy to miss. But if you go from Teatro Massimo towards Politeama, upon entering Politeama turn left (near a kiosk). Walk a few meters and turn left again next to a media shop (you pass under arcades). You will see the shop on your right, just around the corner.
All in all the experience was great and we could not imagine living in a better place. Highly recommended.