Are you interested in history -- the World War II museum is brilliant, and it could easily take 4 hours to see it all.

I have visited New Orleans twice, once for 4 full days and once for 3 full. Loved both trips!

I think 4 full days is a good visit. This will give you enough time to explore and enjoy the French Quarter and Garden District, plus a day when you can visit the plantation and spend as much time as you'd like there. You could do it in three days for sure, but I think 4 days lets you do what you want without feeling rushed.

In the end, I would just look at some trip reports, decide what you want to see/do/enjoy, and go with your gut. Some people probably spend a week in New Orleans and wish they had more time. I knew a few who spent one day and were eager to go someplace else. I think 3-4 days is a very nice and full visit but, as always, that is based on my own opinion and personal travel preferences.

Have fun! It is a great city!

You'll want to stay more than 3 days. I think Shandy's suggestion of at least 4 days is a good one. Then, on the 4th day you'll wish you had planned to stay another 4! Enjoy your trip. I miss New Orleans daily.

I spent 9 days in NOLA the time I went, and filled it fully with things to do. See the latter posts for what I actually did while there:

http://www.fodors.com/community/united-states/new-orleans-itinerary-184065-2.cfm

4 days is ideal. If you stay longer than 4 days you will never want to leave.

We spent 5 days and that was just about right for us.