Rueben's is a family favorite and we take all our first time Montreal visiting relatives here. They have good burgers and steaks, the portions are quite reasonable. It is a bit toward the pricey side and the biggest drawback would be the waiting time. Try going there a bit earlier if you don't have a reservation or you have a big group.
Their desserts aren't the best, I found their cake to be dry.
The service is a good and we always have an overall amazing time at Rueben's.
I would definitely recommend this place to Montreal first timers.