The metro is very reliable. However the bus system is not. I live in the west island where the buses come infrequently and they often do not show up. I rely on their service to commute every day, and it happens too often that the buses are either very late or just don't show up at all. Some days, my bus will just not show up for hours and I have to pay the price.
Again, the metro is wonderful. But the bus system needs more work.