I spent 2 nights at the Radisson Blu and have no complaints. My room was a good size with high ceilings that made it feel even bigger. Everything I needed was there - comfy bed, TV, coffee maker, a good sized desk and free internet access.
The location couldn't have been better and Circular Quay, the Botanic Gardens, and Opera House are within walking distance. If you need to go further, Wynyard station is right there.
I paid $250 a night which is very reasonable for downtown Sydney.