I was long intrigued by the Park Hyatt, having stayed many times across the street at the Four Seasons. Decided to give it a try last Labor Day and again this month, because the Four Seasons moved to a new location and is now ridiculously expensive. I could not have been happier with this hotel on both occasions, and only wish I had tried it out sooner!
Public areas are crisp, quiet, elegant, clean and tasteful, and smell cool and fresh (eucalyptis & mint) due to the adjacent Park Hyatt spa. I cannot imagine that walking into heaven could be nicer than walking into the lobby of the Park Hyatt after wandering around Toronto on a hot, muggy day. Check-in/check-out is quick and efficient, and elevators are are always available within a minute or two at most. Both times I have stayed here I've been in the north wing which is newer, and even a basic king room is spacious and quiet. The housekeeping service is very good as well, my room was always made up very well when I came back in the afternoon or when I returned from dinner/drinks in the evening (for turndown service). Bathrooms are also very nice, with a good selection of products. GREAT wireless internet (free) and air conditioning, and nice soft beds. The rooftop bar on the 18th floor of the south wing is also wonderful and a must-see, it's got the best view of the Toronto skyline in the city. The terrace there is a little crowded on weekends, but not too bad on a Sunday or weeknight.
My only cons are the plumbing in the showers may be getting a bit funky, both times I stayed the water pressure went up/down and the pipes seemed to occasionally shudder a little. Also I'd avoid the restaurant on the first floor, it seemed expensive (particularly for breakfast), and I'm sure there are better bets around Yorkville. These are small issues though, and I wouldn't ding the hotel so much as a half-star for either of them. The hotel is also not close to downtown or the Theatre district, which is fine with me (I much prefer Yorkville, which is cleaner and safer), but if you want to check out Eaton Centre or a show, the Museum subway stop is less than a five minute walk, and can get you to wherever you're going more quickly and for much less than a cab.
Finally--and this is the best part--this hotel has extremely reasonable rates, probably the best in Toronto for a hotel of its class. Both times I've stayed, Expedia has had a third night free after two nights, which knocks the average nightly rate (excluding tax) down to not much over $200 CD, only about $50 more than what you'd pay for a hotel of much poorer quality/service (see also my recent review of the Courtyard Marriott on Yonge). I definitely recommend you give this hotel a try, you will not be disappointed!