The past two times I've been to Montreal, I've visited Commensal. I prefer the location on St-Denis over the one around McGill, just because of the atmosphere; it doesn't feel as cold and sparse as the other one.
The buffet has a good variety of hot and cold foods, as well as some desserts. There's not really anything I would call too exotic on the menu, so with that said, the food here will probably appeal to vegetarians and non-vegetarians alike, as well as different age groups. Some of the menu items are kind of bland tasting, but others make up for it.
Food is priced by weight, which can get a bit confusing, all you can do is eye it and hope it doesn't come out more expensive than you intended. Regardless, the food here is affordable.