There is luxury and there is luxury. If you remember that you are not going to a "first world" location and can put up with the odd power cut and the odd bit of p00 flowing across the roads when it rains then you will have a great time. And when it rains - it really does rain. Not for very long but very hard.
Get a hire car - the roads are like ice rinks even in the dry. Lots of fun.
Best time to go is this month especially if you are a motorsport fan. The Barbados Rally Carnival is a fantastic event. The UK competitors have just shipped their cars this week.
Even though you're going all inclusive make sure you get out and about don't be slaves to the hotel. Plenty of great places to eat and drink.
Good places to go out in the evenings too. If not down the strip then the Boat Yard or Harbour Lights.
Learn to drink rum (preferably XO) and play dominos - you will make a heck of a lot of new friends!
I have a lot of friends living there, one of them flies helicoptor tours, let me know if you need any info.