Hey everyone!
I’m hoping I can get an official answer here, and not just speculation from fellow fans. 
I’m sure there are certain things – such as Achievements, unlocks, bonus cutscenes, Easter eggs, et cetera – that will only happen on Legendary. But is there anything special that we would only get by having our first Campaign playthrough be on Legendary? That seems like a silly concept to me, but I wanted some feedback.
I do plan on doing Legendary at some point; it just might not be my first playthrough.
Thanks! 