As an American I have to say I've been pretty disappointed with most of the burgers I've had in Montreal. I just don't understand why they don't ask what temperature I want my burger cooked, and then cook it to medium well/well done every time. However, Burger Bar DOES ask, and as the first place I've been to that asked (and cooked it to a proper medium rare) they automatically were ahead in my book.
I had the poutine burger, which was really impressive to look at and really delicious to eat. The poutine is kind of like a cylinder of french fries fried together with gravy and cheese curds. I was really impressed with how well it stayed together while I ate it (with a fork and knife.) I got it with a salad instead of fries because that seemed more reasonable. Everyone I ate with also said they enjoyed their burgers.
Our waitress was super nice although the food came out a bit slowly. We went on a Tuesday or Wednesday night so it wasn't very busy at all.
All in all solid burger, and definitely one of the best I've had in the city so far. I'd go back if I were in the area.