This place is leagues better than you'd expect, minus a few nits.
Wahlburgers is apparently famous on TV and is new to the Toronto airport. In the airport, it sports both a fast food area and a sit-down area, and both are quite nice. Think upscale sports bar. Service is really kind and superb (and I have no idea why others here complain about it). There are a ton of plugs available for solo travelers at the bar, which is a nice touch.
The food here toes the line of perfection. My burger - the "Double Decker" because I'm a secret fatty - was perfectly cooked in that tasty-greasy sort of way, but it didn't fit the bun (I had way too much bread and way too little patty, which is annoying). The sea salt fries were spot on. Both were priced at pretty much what you'd expect for an airport restaurant.
At the end of the day, this is a nice little high-ish-end greasy spoon in the airport, and I was pretty pleased.