Both the "world famous" peameal bacon sandwich and the breakfast sandwich (peameal, cheese, fried egg) are pretty damn good.
There is always a crazy queue to get a sandwich, especially in the midst of summer when tourists read about this place in their Lonely Planet guidebooks.
Regardless, the queue moves along fairly quickly and you can get your hands on a sandwich. The condiments are kept to the side of the Carousel booth and it can be a bit tedious trying to get near them as you wait in yet another queue.
I really do like the country style bun - it's really soft and light, not nearly as stodgy as a hamburger bun.
Overall, reasonable place but there are better, less busy food stalls in the basement of the market.