Spent my impressionable years in New Orleans(college) and experience four Mardis Gras. The college gave us off until thursday after Mardis Gras which was a good thing. N'awlins is a city you either love or hate. I love it, my wife who grew up there hates it, and thus I have not been in over 15 years. Mardis Gras is everything everyone describe. There is a lot of good and bad, but at the end of the day it is one giant party with everything amplified 1000x. If you go be ready for the time of your life, you will enjoy yourself tremendously. Some ground rules need apply:
Stay off the side streets and empty streets.
Do not do it alone, go in a group and stay in a group.
Do not let your guard down. You will be drunk and unfortunately N'Awlins is not a safe city to begin with, and this is only magnified during Mardis Gras.
Try to experience some of the Parades outside of N'Awlins. When I was there Metarie(suburb of N'Awlins) some great parades, as did Lafayette.
If the cops tell you to do something, do not argue, they are working nonstop during Mardis Gras and typically are tired and not in a mood to argue. Just do whatever they tell you to do.
Have fun.
Doug