I was taken by a local expat (5 years in Santiago and going strong) and it was delicious. We were there around 8pm, which is early for Chileans, but it was lively and full and that atmosphere continues throughout the night. We had pisco sours for starters and three pizzas amongst us (4 cheese, chef (parma ham and blue cheese), and the classico). We ate until we were stuffed and had several slices for left-over take-away. Thin crust, lots of cheese, generous sizes. Prices were reasonable and we shared a bottle of wine from the extensive list.
It's chaotic and lively in there with busy but efficient service. We are a bit concerned over the fire escapes - there is ONE door and half of it is locked. They also have the 'liquid' candles on the table (big fire hazard) and lots of kids running around, prams, waiters, chairs and always a line of people at the door. We will feel better when they take away those candles and do something different (lamps, etc).
If you are craving pizza and travelling Chile, this is the place to go. You could have an after-dinner cocktail at the W (nearby). Worth the cab ride from your hotel.