Here's a breakdown : the food at Piatto Pieno is excellent, but the service can get very rough at times. If not for the uneven service I would easily give it a 5 star.
I've been there several times, and the food is consistently excellent. I mostly go for pasta or pizza, occasionally a risotto. The eggplant parmigiana is to die for. And on top of it is BYOB.
I won't go into to many details about the bad experiences with the service (multiple wrong orders, extremely long service) but it had definitely been the exception rather than the norm.
I still have been recommending this restaurant to everyone I talk to about Italian food or good restaurants in Montreal.