Legend may be a bit of a big word and you may expect much more of this than it actually delivers. But it's not about anything you may not already know if you just looked into the whole thing a bit. There are other documentaries which have shown that criminalizing Cannabis/Marijuana is not the right way to go about on the "war on drugs" end.
And while there are some voices that are being used as counterpoints, this mostly is giving us the answer that making pot legal is the only way to go. The whole thing is entertaining though ... and if like me, you never knew about "420", the intro into the movie is giving us a joke into the number thing and the title itself too. And you also have comedians going off on certain stereotypes ... sometimes painting pictures with other stereotypes. All in all this is good fun and decent enough