You get an achievement and gamer score. I get that getting some sort of digital tricket is nice but it shouldn't be necessary if you truly want to accomplish finishing the game on legendary. Do no one have the ambition to do something just to do it, get that sense of accomplishment? Does all task have to have some sort of reward? But guess I am old school that way, when we went through the trouble of beating a game all we got to see are the credits and we didn't have internet to show us any cheats, short cuts, walk throughs or any of that.
BTW there is an alternate ending when beating the game on legendary.
I know what you mean by beating something just for the sense of self accomplishment. I mean, I grew up with sega genesis and NES games where if you died you were SOL, and if, by a miracle of god, you beat the game, you'd get a little -Yoink- pixelated screenshot and a few paragraphs of nonsense scrolling down your TV/computer...
But I have high functioning autism, so I LIVE for little symbols/trinket/marks/mementos/etc that remind me of my efforts. I even tattoo myself whenever I do something significant happens in my life ( not one of those Dbag "luv yu babeygurl " trailr park tats when you marry your 2nd degree cousin types), more like "I forgot my favorite pen in the airplane therefore i need an abstract tattoo that represents the loss of a mechanism that allowed me to communicate effortless without speaking, while symbolizing how my own negligence can rob me of the precious things I take for granted." autism.
sorry for the tangent. But yeah, no big deal, but getting a cool helm or weapon skin would be "kewl" ( do kids still say that?)
just my opinion, of course...