To me, burger places are all the same. South Street is no exception. This comes from my philosophy that burgers and fries are not "real food". Real cuisine would be something like pasta or most Asian dishes that requires seasoning and a cooking procedure more complicated than putting it on the grill and wait. I don't think South Street even marinate their chicken...
I've been to South Street 3 times with a groupon and all I can say is that the quality of the food depends on the person making it. On my first try, the cook severely overcooked the chicken. Of course, I didn't know until I came home. It wasn't burnt. It was just overcooked so it tasted really dry. The second time it wasn't as overcooked. The 3rd time the burger was just about right. Their fries are New York Fries, meaning it's not like McDonald's shoestring. NYF has a bit of skin to it. I like it but it's more of a personal preference than an actual indicator of quality. I had the poutine once and it's not bad. I don't think poutine can ever taste bad. It's a comfort food. Though I think the portion is a little small for their price.
Speaking about price, I think if they chop $1-2 on everything, it'd be more reasonable. Their burgers are nothing special, and I believe I've said this about every burger place I've tried.