Loved it!
I went to Marius while in Rio, 3 yrs ago, and I must say it was a truly grand gourmet experience!
Everything, the beautifully arranged all-you-can eat bar, with all kinds of sea food, meat, various Brazilian specialties resting on hundreds of kilos of ice, main course(s) which the really nice and helpful staff keeps delivering to You freshly done, the wonderfully tasty (and let's don't forget - healthy) squeezed juices, I say everything there is worth a trip to Rio! I'd specially recommend the deserts - the Marius-made truffles are simply the best!
The price spices things up a bit but it's really not that much - 130-160 R$ per person.