What dates? I ask because Mardi Gras is in March this year. If you stick to the tourists areas, you should be fine. But, like a previous poster said, this is a dangerous place!
Stick to suggested places and explore them during the day. With that said, you will probably have a great time. Check out the Riverwalk, Jackson Square, the French Market, and you can ride the ferry to the west bank and back to get a beautiful view of the city from the river. Don't get off, just ride there and back. It's about a 30 minute ride roundtrip and it's free. Hope you have a great time when you come down.