Please do yourself a huge favour and make reservations in advance, at least 2 days beforehand. You could call in or book online, which is very convenient when the phone lines are busy with others trying to make reservations. If not, walk-ins should expect to be waiting up to an hours wait for 2 people on a Saturday during prime dinner time.
With that being said, testing your patience and the will of your stomach is definitely worth the wait! The service is pretty good, waiter service have good knowledge of their food & wine and the food comes out relatively quickly. The atmosphere is industrial looking but cozy, like you're eating in Grandma's pantry in her modern loft in trendy Liberty Village.
I suggest that you book well in advance (emphasis on the "well in advance") and come with a group of friends so you can eat family style. You'll be wanting to try everything on the menu because it's all so delicious! The portions are good sizes too, which can be easily shared. The prices are very reasonable for the amount and quality that you'll be getting, however your bill can really add up because you can't just go to Terroni and not have a 3 course meal with drinks. So save up! Downside is, they cannot separate your bills so practice your math skills people or else you'll be sitting there for as long as you've been eating :p
My growing list of things you must try are:
Funghi Assoluti - oyster mushroom & arugula appetizer
Ravioli di Zio Paperone - duck confit ravioli
Spaghetti in Canna a Mare - various seafood spaghetti
C't Mang & Polentona - Pizzas
Budino di Caramello - salted caramel butterscotch pudding
Torta Calda al Choccolato - flourless dark chocolate cake
Panna Cotta - creamiest and best I've ever tasted