This Denny's, the first in downtown Toronto, opened a few months ago in a newly-refurbished building, more than a year after it was announced. I've come here a few times because I live in the area and it makes sense for a convenient sit-down breakfast or brunch on the weekend. It's rarely jam-packed, but usually there's an even mix of locals and tourists (not shocking since it's very close to the intercity bus terminal and the Eaton Centre).
Pros: Lots of variety, generally good quality, and some of the chain's limited-time offers are worth trying (recent faves include the Double Berry Pancakes and the Cali Avocado Skillet). A few decent healthy options ("healthy" always being relative when it comes to diners) though these tend to be a bit more expensive. Modern-looking location and good atmosphere overall.
Cons: Service can be slow at times, but it has been getting better since it opened. Prices are kind of high compared to the other breakfast chains in the area, especially if you're just getting a basic breakfast (there is no value menu as there is at Denny's in the U.S.) - though this may just be due to the prime downtown location.