I have to start off by saying that I love the Bell Centre for Montreal Canadiens games. I've been to a few different arenas, but none compare to the atmosphere that you get here in Montreal. Fans on their feet, beer in their hands and usually a pretty good game on the ice.
Unfortunately, for concerts, I'm not the biggest fan. First of all, if you're sitting at the top of the reds or higher, it's almost impossible to make out the lyrics of the opening bands. The sound is usually a bit better for the main act, but even then, not very impressive. Although, the sound quality from the floor is good.
There have been a few too many times that something goes wrong with the lines to get in, like the time they delayed entrance to the floor for so long that about 50% of floor ticket holders missed the entire opening act (one we actually wanted to listen to), or that the mics cut out, or that security isn't very helpful when in need of help like a girl who passed out next to me.
If you're visiting Montreal or are from the city, you can't miss it! Go see a show or a hockey game, you won't regret it, but I would suggest spending a bit more money to get lower seats for concerts.