For getting the achievement INFINITY i have to play the whole campaign?!
I don't got the achievement INFINITY for beating the fourth level on any difficulty.
For getting I NEED A HERO (heroic solo or coop), THE LEGEND OF 117 and LONE WOLF LEGEND at the end of the game, you have to beat the whole game solo on legendary difficulty!
But that's my problem - if level infinity isn't displayed as beaten in the campaign-level-selection (DAWN, REQUIEM and FORERUNNER are displayed as beaten on solo legendary) - i think i can play the rest of the game but i will not get any of the achievements above - cause one level-completion and the achievement for this level (INFINITY) is missing!