I've never actually been to Massey Hall as a patron/concert-goer. I've only ever been on stage. As an acoustic venue it sounds great. Plus all the balcony seating is up close so you can very easily connect with your audience.
However the back-stage facility is HORRIBLE! The dressing rooms are few and far between and some even have fixtures/plumbing that look like they were installed in the 1930s. The green room is bright and airy but not nearly large enough for most of the contraptions that bring me to this stage.
If you're travelling to this venue by stage-coach, make sure you tell your vallet what time the concert will be over as there is no pasture close at hand for your horses. You can of course park your conveyance at the nearby lots to the tune of $18-$25 to escape.
If you ever find yourself on the tech portion of a tour coming to this hall make sure you keep clear of the "loading dock" until the strong-arm union crew is on shift or else you face extra charges. (By loading-dock I mean the street out front! Horseless carriages came 20+ years after this place was built)