I've been to a lot of shows at the Bell Centre, not my favourite venue but not the worst... sight lines aren't bad and acoustics are ok for a hockey arena. I guess my main dislike is that it's kind of a soulless corporate space. Unfortunately there really aren't any other alternatives in Montreal for big shows. Beer and food prices are ridiculous and quality is dubious, eat/drink before you come... I've found most of the staff to be pretty decent with the exception of one security guard who hassled me for not leaving fast enough when I was seven months pregnant...
One big positive about the Bell Centre is that it's very accessible by public transit.