The Hollywood Reporter has the news:
The series, starring Clark Gregg reprising his role from The Avengers, debuted Sept. 24 against stiff competition from The Voice and NCIS premiere to a 4.7 rating among adults 18-49 and 11.9 million viewers, ranking as the top network drama premiere since ABC’s V in 2009. Opening the night at 8 p.m., it topped both Voice and NCIS episode in the demo. The series ranks as the No. 1 series of the 2013-14 season among adults 18-49 (4.0 Live+Same Day, 5.7 Live+3). On average, Agents of SHIELD is No. 1 in its Tuesdays at 8 p.m. slot and has more than doubled the young adult demo in the hour year-over-year.
The second and third weeks didn’t fare quite so well, but the full season order means ABC has faith in the series the bounce back and they also recognize how big a deal it is to have a Marvel series in Prime Time.
This also makes Agents of S.H.I.E.L.D. the first Joss Whedon television series to have a 22-episode season since the fifth season of Angel.