I kind of enjoyed pizzadelic as well, but I've only been there once. But you're right, it's not really a "classic pizza". There is definitely a lot of cheap ass food in general in Montreal though, so the fact that there's cheap pizza isn't really that big of a deal.
I'm ashamed to say that I haven't really had pizza too many place here in Toronto, but I definitely like Amato, although I'm disappointed they don't sell the Capri (tomato sauce, mozza, chicken, green onion, mushroom, rosemary & goat cheese) in slices anymore! There's a few places that have been on my "eat there" list for a while, but I've just never gotten around to it.