Out of the Blue is a masterpiece!
Seriously, I would put it amongst the top 25 greatest rock albums of all time. The "Concerto for a Rainy Day" suite is the band's greatest moment.
A New World Record and Discovery, while not nearly as good as Out of the Blue, are also both outstanding albums, albeit very different. Outside of these 3 albums, there is a dramatic fall-off in quality. Which isn't to say they're bad, just not even remotely as good as The Big Three. Remember, if it has the "jukebox logo" on it, it's fabulous!
P.S.: Bev Bevan is one of the most underrated drummers ever!