Yes, this place is very busy, and at peak times it can be difficult to find a seat. If you are looking for quiet intimacy, it ain't gonna happen here... but if you want an uptempo contemporary vibe and excellent - I mean excellent - choices for Portuguese (and world) cuisine then don't miss it! We went here three times for supper during our 5 days in Lisbon. We recommend that you hunt for seats first (never took more than 5 minutes to find for us) and then one will "hold the fort" while the other(s) go to order.
My favourite was the whole chicken (Portuguese style) at Miguel Laffan - and my wife enjoyed the goat cheese salad with honey ice cream (!) at Cozinha da Felicidade. Hint: don't order your drinks from the restaurant with your food - order your wine and/or beer from the little place just outside the northeast corner of the food court (to the right of Miguel Laffan) - it is cheaper and quicker and you can bring it to your table separately.
The market is right across the street from the Cais do Sodre metro station.More