I am a fellow at McGill and this is one of the most exciting places in the area. This is not one of your trashy students joints, this is a classy student hang out club. Once your foot will step in this place you will automatically know what I mean.
You have a nice small bar, a few lounges you can still in armchairs or sofa's to work or relax, a ballroom for events upstairs and in the basement another nice big location that during the weekends you have societies events there and during the summer everyone are at the sunny tables enjoying life.
This is a student place so the prices are EXTREMELY reasonable, I would even say cheap. The best chill and have a nice conversation place near McGill.
So you are wondering why only 4 and not 5? well it is located in a place that basically when you go there you can only go there, you wont find another close pub if there is no room or you want to change atmosphere.