Very comfortable, though a bit noisy at night on the weekends (McGill students walking home). This is a student's apartment, not a hotel room, but it was clean, comfortable, and inexpensive. Kevin is a wealth of information for US students who may be considering McGIll (he's from NJ).
There's an underground parking garage attached to a grocery/food/cinema complex just steps away.
To avoid roaming charges, I suggest purchasing a short therm plan that covers your time in Canada.