I stayed at Grand Hyatt Athens in October - it's the only Hyatt hotel I've stayed at to date that I would classify as an utter dump. Probably on par with e.g. Grand Hyatt New York from what I understand of that hotel, it's a basic four star hotel that somehow got branded Grand Hyatt. I'd be more than happy to pay 3x the price per night to stay at Grande Bretagne unless I was really desperate for the extra space from a suite.