Grade and texture of the meat. Moistness. Tenderness.
I haven't been, but two points:
1. The "Wilensky" is named after Wilensky's Light Lunch, a small diner on St. Viatuer made famous by Mordecai Richler in The Apprenticeship of Duddy Kravitz. The sandwich at the original deli is pressed swiss cheese, all beef salami, mustard, and bologna on an onion roll. It's a charming anachronism but it's not worth a special journey, as they say.
2. Sometimes the artisanal version misses the point. I had poutine at T-Poutine for the first time the other night - the dish took the guy ten minutes to make. He tossed the cheese curds with the the gravy in a pan and poured it over fresh, crispy fries. It was a total failure. The fries in real poutine are skin on and half soggy and the cheese curds are not melted. It's a slapdash dish and that's what makes it great. You're supposed to be able to jam fifty fries and twenty cheese curds on a plastic fork and jam it into your mouth. Your not supposed to twirl melted cheese daintily around a crispy fry. Sometimes, extra refinement is detrimental.