Someone mentioned a few pages back, rightly so I believe, her trepidation with Banner was contrasted by how she manipulated Loki. She uses her feminine wiles as an agent and she could never get a proper bead on whether or not she could "seduce" Banner because of the unpredictability of the Hulk.
If she is then the "human/normal" element and the humor of the stand alone films will suffer. Coulson is a much needed character and Hill ain't up to the job.
Also, speaking of Tony through the portal and the shots of his eyes reflecting the stars and blast... I haven't seen Sunshine but I kept waiting for a "My God, it's full of stars" line.