You haven't missed anything. St Catherine's street is all the nightlife you get in Montreal. As a resident of Montreal in my opinion, a tourist will find the city good for a week or so partly because of its unique look n feel European style. After that the reality of Montreal's worn down infrastructure kicks in. I would say Montréal is just riding on its old glory days before Bill 101.
My wife is a Montreal native and we go there once a year to visit her mother. I love it there but it has it's downside like every other place. The roads are horrible and the traffic to get on and off the island is insane. Hopefully the new bridge will help. I think having a French speaking partner along with you makes the experience much better.
