Both luxury and luxurious are used as adjectives.
'Luxurious hotel' means a hotel which is more likely to be expensive, enjoyable and comfortable i.e. it describes the condition of the hotel.
'Luxury hotel' is more to do with the standard or class of the hotel the owner wishes to project as an image. A 'luxury hotel' is supposed to be of superior standard compared to say, a budget hotel, and it claims to provide 'luxury'.
You can draw a parallel with the words, 'comfort 'and 'comfortable'.
Comfortable is the adjective used in most situations. You also hear of the word 'comfort' in special cases like
comfort home - an euphemism for 'old folks home'
comfort woman - woman forced into sexual slavery for the Japanese during World War II
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