I visited Mercato for the first time on a Saturday evening. Our group reserved for four at the counter a couple of weeks in advance, a definite MUST if you want to assure yourself any seat in the restaurant - the place was packed.
The food was very good although you would not have a great deal of choice if you were a strict vegetarian. If fish is in your diet, you're set. I loved the casual platting and option of communal eating - our group of four shared everything. The wine we chose was wonderful too.
The ambiance was great. I highly recommend sitting at the counter so you can watch your food be cooked and prepared. Keep in mind though that if loud isn't your thing, this is not the restaurant for you.
The price: We shared 2 appetizers, 2 starter meals, 2 main courses, 2 deserts, and 2 bottles of wine. For four people, the bill ran over $360 with tip. Mercato means a special dinner out for us.
I recommend you visit Mercato at least once to enjoy its atmosphere, food, and energy. I'll be going back the next time we have a special occasion to celebrate.