Not sure I can improve on the combined wisdom of 771 previous reviewers, so here's the upshot:
.:. Horrendously long lines. Order from the to-go counter instead, where there's no line and almost always a couple of chairs in the back. Or eat standing up. It's not worth the hassle of waiting for a table.
.:. "Smoked Meat" is really just brisket. It's a little on the salty side, but has excellent flavor. I recommend a medium fat level: the lean ends can be dry but the fatty ends are practically inedible.
.:. Rye bread and spicy mustard: YES. Classic Jewish deli food! Just don't tell the Canadians they didn't invent it. :)
.:. Fries: average. A little on the dry side. I'd skip them in the future.
.:. Price: a little high for the quality, but not bad. Worth doing once, if only so people will stop telling you it's a necessary element of your Montreal experience.