This Home Depot is not your parents Home Depot (assuming your parents live in the suburbs that is), as it's not a massive warehouse in a power centre where the next closest hardware store is the Rona across the parking lot or the Canadian Tire across the 6 lane thoroughfare. In fact this HD connects internally to a mall (Gerrard Sqaure). So right from the get-go you need to go there with the understanding that they won't have absolutely everything you've come to expect from HD.
As far as downtown TO goes it's about as good as you're going to get though. I can't really comment on the prices because I'm not a contractor, but they seem to be decent and there are always a lot of tradespeople in there, so I would assume that constitutes some level of endorsement.
I have found the staff to be generally helpful and easy to find. Though I will say that they don't seem to have the hiring standards that other HD's (i.e., my parent's HD) have. For example, it doesn't appear that the staff members are a bunch of semi-retired tradespeople who know a lifetime more about my project than I could ever know.