In the 22 episodes of season one, the show's creators not only worked within the constraints of what had already been determined as S.H.I.E.L.D. in the Marvel universe of comics and movies, but also the explosive destruction of S.H.I.E.L.D. in Captain America: The Winter Soldier. In season two, executive producer Jed Whedon explains, they get to redefine S.H.I.E.L.D. completely. "In a way, it's the first time we have our own universe to build that's not just in the cinematic world they've already created." Prepare for anything and nothing that you've seen in a comic before.
Source: Twitter user POPSUGAR Tech