Have been to Nassau twice. A few notes:
Atlantis is the big attraction there. It's a huge resort - you've undoubtedly seen commercials on TV. The aquarium is pretty nice, although nothing special compared to some of the nicer ones I've seen in the states. The water park is really good, though. If you like water slides/etc, this is where you should go for the day. Food in Atlantis is ridiculously expensive, though.
The area around the port is bustling with "stuff". It's a fun hour browse. Oh, and those "Cuban" cigars advertised on the signs are not really Cubans. The cigar shop in Atlantis has real Cubans, though.
Do not venture more than a block or three away from the port, though. It gets very seedy, very fast. Nassau is incredibly poor. The bar at the end of the first block (I forget the name - frog something) is decent.
We took a cab to and from Atlantis (there are hundreds of them all around the port). Seemed legit, but there was a small part of me wondering if they would drive out to the middle of nowhere and say "ok rich American, $100 gets you back."
It was fun for a day or two, but the next time we stop there on a cruise, we'll probably stay on the ship or just hang around the port area - we've seen enough of Atlantis, and the rest doesn't interest us that much.