Story, reason below
As long as the graphics are better than halo 1 (the original from 2001) then I am happy with the graphics so I would probably say story is more important, however it is good when you get both because graphics help create atmosphere. I would rather a game with good graphics and good story with bad gameplay over a game with good gameplay and bad story, and bad graphics (Good example is mass effect 1 had good graphics and story but bad graphics and I would take it over COD5 any day). it's nice when it's a game like crysis, halo or mass effect 2 were you get all three (I don't care for multiplayer)
As long as the graphics are better than halo 1 (the original from 2001) then I am happy with the graphics so I would probably say story is more important, however it is good when you get both because graphics help create atmosphere. I would rather a game with good graphics and good story with bad gameplay over a game with good gameplay and bad story, and bad graphics (Good example is mass effect 1 had good graphics and story but bad graphics and I would take it over COD5 any day). it's nice when it's a game like crysis, halo or mass effect 2 were you get all three (I don't care for multiplayer)