I was never in the first tier of Joss Whedon fans. I came late to the Buffy the Vampire Slayer party, and I found Angel, Firefly and Dollhouse unappealing. Whedon's film of The Avengers did impress me, though, and I liked the Agent Coulson character (he was in the Iron Man films, too), so I hoped Marvel Agents of S.H.I.E.L.D. might be worth watching. After seeing three of the first five episodes, I conclude, "I guess not."
     S.H.I.E.L.D. has been around the Marvel Universe for a long time. It started when Marvel wanted something to do with Nick Fury in the present day since his World War II adventures were so popular in Sgt. Fury and His Howling Commandos. They tested him in an issue of Fantastic Four, where he was a CIA agent, then gave him an ongoing series in Strange Tales as director of S.H.I.E.L.D. It was mainly an espionage book where Fury, despite being the director, was always in the middle of fights and action. His primary villain was Hydra, a spy organization that was (retconned to having been) formed by surviving Nazis after the end of WWII with the goal of world domination. He also faced Baron Strucker, an actual Nazi (I think) from Fury's WWII days and other villains with super scientific weaponry out of the James Bond films. Later. there was a long and involved storyline where Fury faced the Yellow Claw, a literal "yellow peril" bad guy from the 1950s and Fu Manchu ripoff that would have been more offensive if he hadn't turned out to be a robot manipulated by Marvel's number one baddie Doctor Doom as a real-world game.
     Eventually Fury's comic was cancelled, but S.H.I.E.L.D. continued to appear in virtually every Marvel comic at one time or another (primarily Iron Man, Captain America and The Avengers).
     None of this has anything to do with the current TV series, which doesn't seem to be based on any of the comic book incarnations, and is bad and boring in almost every way, especially acting and writing.
     Agent Coulson, who died in The Avengers film, is back, though it's suggested that he's not what he seems. I'll probably never find out because after watching the first two or three episodes, skipping the next two and giving it one last chance last night, I'm through. The S.H.I.E.L.D. agents on the show are totally uninteresting. The criminal organization behind everything is called Centipede (maybe a Hydra substitute because Hydra is tied up in one of the film franchises?) and is using a variation on the Extremis formula (from Iron Man 3) to create superhumans.
     The main problem, again, is that the writing (particularly the dialogue) is bad and/or boring, and the actors are unable or unwilling to rise above the writing's limitation.
     That's the main problem, but there are others. For one thing, the series follows not the activities of S.H.I.E.L.D. but rather the activities of a small group of S.H.I.E.L.D. agents, and there seems to be no reason  for this particular group to be together, or for us to follow their adventurers. Their mission is diffuse, imprecise, unfocused. They are vaguely following Centipede's actions, and a computer hacker organization that is either connected or being exploited by Centipede.
     There has been fake drama in that one of the team is a member of the hacker organization who has infiltrated the team for some mysterious reason (now revealed to be a search for her mother), and what is the secret behind Coulson's resurrection. There are several possibilities:
     He might be a robot. In the Marvel comics, S.H.I.E.L.D. has realistic androids called Life Model Decoys, or LMDs. Is Coulson one of these? Maybe. Maybe he was one all along.
     He could be a clone. Marvel has long had clone technology, so maybe Coulson was cloned from his  own dead body.
     Time travel. Maybe this Coulson is from an alternate timeline. Marvel has long followed the idea of the multiverse, an infinite number of parallel universes, sometimes different from our own only by a single incident which then diverges, butterfly effect style. This is less likely, since Coulson remembers his death.
     I'd better stop here or I'll make the show seem more interesting than it is.
     Whedon's done better, including Buffy Seasons 2-5 (and some of 6) and Dr. Horrible's Sing-along Blog, but this show is a mess. The good thing for the show is that it has a full-season pickup, so it might have time to improve. I won't be watching, however.