I was in Nassau for about an hour and went back to the ship. The streets are horrible, no curb cuts, most of the stores you can't get in because of a step. You can also forget taxi service to places like Atlantis.
I mean don't get me wrong, maybe I didn't give it enough time. I wanted to go to the straw market, but was so frustrated I just wanted back on the ship where I know I could enjoy at least the sights, movies, food. I spent most of my time on deck 4 outside enjoying the sunshine and warm temps and people watching. Also had a great book and MP3 player to keep me company.
I would suggest you at least try to see some of Nassua, if it doesn't work for you just head back to the ship.