We stayed for a month in Mario's apartment in September, which is quite a nice time to visit Gozo weather-wise. The apartment is exactly as shown, and everything is very well equipped for a long stay (good kitchenware etc) and the use of a swimming pool is really nice. There is also a supermarket and a couple of good bar/restaurants in walking distance. Our only small issue was that the apartment could have been a little cleaner upon check-in (but nothing too bad) and some more detailed instructions as to where to find the place (perhaps a map?) would have made our arrival easier. Overall though we would highly recommend it.
A small house tip - As the tap water is potable but has a pretty bad taste, you might want to buy a Brita filter to fit the Brita jug that is in the kitchen (about 6 euros) - cheaper even for a weeks stay I'd think.
Re: the area in general, Gozo is not a bad place, certainly less busy/polluted than Malta, although not quite as rural/unspoilt as we prefer personally - but that's just personal taste. The apartment is a great choice if you are staying in Gozo and is well connected to the rest of the island by public transport.