The famous Mamasita corn is indeed very good. Yes it's only corn, yes it's expensive for corn, but if that's how you feel, make it yourself and don't order it. I'm happy to order this dish again as I'll eat good food any day.
Other items that were pretty good but not amazing were the ceviche and the quesadillas. They were the two weaker dishes of an otherwise excellent meal.
Another item Mamasita is famous for is their tacos. And they did live up to expectations and were great. The tostaditas and potatoes were also really good. The pancita de cerdo recommended by the waiter was excellent.
Overall, the food was really good and I would go back. The service was both good and not so good. The staff were friendly enough but it was so hard to get their attention when we wanted to order, to ask for water or even to pay the bill.
The atmosphere in the restaurant is good but I actually don't really like the layout of the restaurant. Obviously space is at a premium in the city so seating is close, which I don't mind. We were at a high table and like many places, I hated the bar stool type chairs as you can't lean back and after a 2 hour meal it gets quite uncomfortable. Overall a very good meal and I would definitely recommend it if you're the only other person in Melbourne who hasn't gone yet.