Probably one of the best politicians that could come out of that country. He's a prime example of using power to benefit the poor, and being accused of being "authoritarian" because he went outside of traditional norms of bourgeois-democracy to do it. In a really good Ken Burns documentary about him, his son states that his opponents criticized him of abusing the "forms" of democracy, when Long cared about the facts of democracy: uplifting the standard of living of the poor of his state.
Populism can mean demagougery, but even if it applies to Long's case, it doesn't matter, because of how he used his position. I think its hard to deny that he didn't live up to, or practice his "every man a king" rhetoric, his policies had the elites of Lousiana so pissed off that they eventually assassinated him for it. FDR didn't go nearly far enough with the new deal in his opinion. The poor of Lousiana loved him for generations; Huey P Newton's parents named their son after Huey Long.