In comparison to other Canadian (and other International airports) Toronto's is simply meh.
I've flown into YYZ on numerous occasions since before I can remember. It's either during the summer or the holidays, both which can be very busy times at the airport, so I do keep that in mind. However, for being one of Canada's biggest airports and a central hub, I'd expect YYZ to be at the top of its game. But, it's not.
Wifi: No complaints about the YYZ wifi. Fast, easy to connect, and didn't disconnect every 10 minutes.
Bathrooms: Not the cleanest airport bathrooms I've seen, but also not the worst. Nothing special here.
Signage and Navigation: Easy, breezy. There are numerous signs everywhere that lead you to your gate and washrooms. The worst part about an airport is if they don't have good signage to get you to your gate. Good thing YYZ doesn't have this problem.
Restaurant options: I usually hang around the domestic terminal because I'm usually flying from Vancouver. Aside from Tim Hortons, Subway and Booster Juice, there are very limited dining options on the domestic end. I saw one restaurant called Tap & Pours close to the B1-B5 gates, but other than that it was one of the few actual sit down spots.
Overall, YYZ is just an A-Okay airport for me. Nice staff, good wifi, and easy to get around.