I stay here fairly regularly. I'm fairly sure it was Perth's original five star hotel, built in the mid-1980s as the Merlin before Hyatt took it over not too many years later. It underwent a full makeover of all rooms about four years ago. The rooms are large and spacious with very nice decor. In an act of design stupidity the power points deactivate when you remove the keycard from the reader meaning you second a card if you want to charge your devices when you're out of the room.
As far as Hyatt Regencies go it's great. There are a number of decent restaurants. The pool area is fantastic and receives a lot of sunshine. The Regency Club, as noted, isn't large but there the canapes are excellent and a number of alcoholic beverages are available. Diamond members are eligible for a very reasonable $15 upcharge to a full breakfast.
In my experience, service is like most five stars in Australia. Okay but not at all polished.