Must agree with Linnyann, the restaurant directly opposite is excellent both the food and service. It is called Da Rosita. Unfortunately, we did not visit until our last night but it will be first on our list next time.
We have been to the Fish Restaurant many times but it has gone slightly down hill over the years. One of the best things about it is the outside tables on a summer evening - there is no better location in the area. They used to have a guitarist or a pianist playing in the evenings at weekend which added to the ambiance.
We also enjoyed Nostalgia which is just up the road from the Gillieru. There is also a newer restaurant which you can see from the front steps of the Gillieru. It is up a slight hill to the right. I think it is called Don something. We we went there three times - the first two were absolutely excellent - the food was superb but on the third occassion it was a very busy Saturday night and we walked out after our starters because the service was so appalling. It was such a shame because the food was good.
Must do for me would be a trip to Gozo.