I recently took a trip to the Bahamas, and decided to check out the infamous, Atlantis Hotel located in Nassau.
The first tip I can advise is, do your research! Encompassed in Atlantis are about 5 separate hotels, all umbrella-ed under the parent company that is Atlantis. The comfort and luxury level of the resort vary drastically from tower, to tower. Starting with the much more affordable Beach Tower ($250-400/ night) to The Cove ($450-700/night). (To visualize- the beach comparable to that of Circus Circus Las Vegas and the Cove is comparable to that of the Aria).
I would certainly recommend staying at The Cove. Why? Excellent commendations, complete with complementary sandals, a private pool, upgraded rooms with large patios and exceptional ocean views. Please heed this advice and do your research! Just because you are staying on property at Atlantis, your experience could be insanely different, dependent upon where you stay specifically.
Who should visit Atlantis? This place is truly great for families, or anyone traveling with children. Skip this if you are a couple, or single group of girls/guys. A plethora of water slides, and activities not exactly romantic or ideal for a girls trip.
What to do? Dine at The Bahamiam Club, and Olives. Shop, (tax free)! Enjoy the pool at the cove, and sit on the beautiful beaches.
How long to stay? 4 nights is plenty. 
LA Donna 