How the show's writers and producers managed to turn that (invisible space-)ship around isn't so simple as a casting shakeup or a change in mission statement. The problems with Agents of SHIELD were numerous and baked into the show's very nature. They weren't going to be quickly fixed.

The Old Characters

The biggest problem facing SHIELD after its first few episodes was that it was boring. It had that spark of Joss Whedon-esque dialogue, sure. It had Agent Coulson back from the dead, which was great. But who were these bland stiffs surrounding him?

There was Agent Ward, a white-bread guy who seemed like he’d probably been an underwear model (fine, actor Brett Dalton was an MFA from Yale, but come on). There was Skye (Chloe Bennet), the hacker girl, which: Name the last good TV character who could be accurately described first and foremost as a hacker. Impossible. You knew baby-faced techies Fitz and Simmons (Iain de Casestecker and Elizabeth Henstridge) were bad characters because their only characteristic was that their names together made FitzSimmons. That's the joke. The one semi-bright spot was Ming-Na Wen as Agent Melinda May, a somewhat standard, taciturn ass-kicker who was at the very least watchable. This was the team we were supposed to follow around the globe, chasing after sub-Loki villains and talking about how Thor did that thing with the hammer one time, you had to be there.

By the time I had checked back in near the end of Season One, things were a little bit better. Agent May was still the most interesting character, and by a wider margin this time due to her double-agent-or-not storyline, but signs of improvement abounded. Skye, as is the destiny of a character like hers, was getting more competent and less aloof with every episode. Ward was working a moral-ambiguity thing that had promise. FitzSimmons were still just the kids, essentially, and Coulson was mired in a how-am-I-alive/who-am-I plot that had long since gotten stale, but there were reasons to care about these people poking out from the margins.

Cut to the current timeline, and every single character is more interesting. Agent Ward went full villain—albeit one the show is clearly keeping around for a possible redemption—turning the show's dullest weapon into its main source of conflict. Skye became (1) an actual SHIELD agent (for, like, one day before the Hydra bomb dropped) and (2) the subject of some intriguing backstory to be revealed later. Fitz and Simmons were dropped to the bottom of the ocean, and the escape left Fitz brain-damaged and Simmons at a loss for how to fix him, instantly giving reasons to care about both of them and making Fitz arguably the most sympathetic character on the show. Coulson's resurrection angst turned into something else again—we haven't gotten there yet as to what that something else is; he's probably an alien; it's fine. These are people viewers can care about now.