Louisiana is kind of two states in one.
South of US-190 / Opelousas is Cajun country, and most of the post so far have been about that area. It is fantastic fun, and really different from any other area in the US.
North is a hilly woodland, with big farms along the Mississippi. Some very nice state parks, and interesting cities. Natchitoches is the gem of that region. Some really nice tours and such.
In my view, the best plantation homes are in Natchez, Mississippi. For one thing, they are close together, easy to see several. They were the homes of plantation owners, who commuted across the Mississippi River to the huge farms in Louisiana. Many of those farms are still in operation today. It is an amazing drive along US 425 or US 65 when the cotton is near harvest.