Dar Isla is a very nice place. The hosts have put real effort into it, especially the interior decor. It is also super clean and well equipped with everything one might need. The only thing one must bear in mind that there are lots of stairs, the apartment is on three levels and the main bathroom (cozy and clean in itself) is down below (but there is another toilet nearer to the bedroom, so no worries really). The narrow streets are rather noisy, but that is part of the local atmosphere and actually is quite charming.
The neighbourhood is really authentic, not touristy. However, there are good restaurants down by the marina. Both Senglea and Vittoriosa across the bay are wonderful little gems, a bit off the beaten track.
Alessandro and Romina are caring and good hosts. The welcome pack with some essential food gets you started on the first day. They communicate very quickly, both before the trip and during that, whenever you have question, the reply is prompt to come.