If it isn't clear already, Whedon has gained the colossal cult following he enjoys based on his writing, but specifically for the characters he has created. With Buffy the Vampire Slayer, and again in Firefly and Dollhouse, an ensemble cast of incredibly diverse (and opposing) characters were lumped together, and intent on making things work. That might seem like a fairly broad description, but even from that perspective, AoS is - on an individual character basis - coming up short.
Casual observers and Whedon acolytes alike will credit the writer with crafting 'quirky' characters, possessing offbeat or oddball character traits, making them more relatable or at the very least, more entertaining. But what is so often perceived as 'eccentric' or 'quirky' is the realization of a character that simply can't be contained in a single stereotype. And although Agents of S.H.I.E.L.D.'s cast may contain direct analogues to Firefly's on the surface, weaknesses are starting to show.
Start with leading men: Nathan Fillion's 'Malcolm Reynolds' made the actor into a geek icon, but the character itself is the hardest to define out of the entire show. A professional thief and smuggler with a moral compass, a defeated rebel who demands obedience from his crew, and a man who will do whatever it takes to live another day, but still crack a joke when staring death in the face. That is the kind of character that can carry a series, since viewers will tune in just to see how unpredictable he'll be.
With Whedon's current team effort, that load seems to be shared by Agent Coulson (Clark Gregg) and Agent Ward (Brett Dalton); Coulson the fearless leader, and Ward, the man of action. The problem: Coulson's entire character was designed to be so one-note, fans still debate whether giving him the spotlight was good for either the character or the Marvel universe as whole (but that's a conversation for another day). The only interesting aspect of his character is a mystery that is promised to be explored 'sooner or later.'
Similarly, Ward fits so easily into the 'no-nonsense lone wolf' that there's little room to work with. And the problems don't stop there.
Malcolm Reynolds' right-hand-woman Zoe (Gina Torres) proudly stands as one of Whedon's Warrior Women, as deadly (if not more so) than her captain, without actually needing to throw a punch - her backstory in the military gets the point across. That same role presumably falls to Agent Melinda May (Ming-Na Wen), Coulson's own right-hand-woman and 'driver of the bus' - a character who perfectly illustrates how Whedon's heroines are much, much more than 'tough women.'
Zoe was the strong and silent type, but she was also a wife. When the job was done, she returned to her (shorter) husband, revealed vulnerability, and showed an entirely different side of her character. Melinda May has a relationship with no one, a general disdain for having to interact with anyone about anything, and again, exists to fulfill plot requirements.
What's her story? We'll get to that eventually. But isn't she cool when she punches??
The same issues are present with the rest of the cast, with the duo dubbed 'Fitzsimmons' knack for science, numbers, and problem-solving - all while being so darn adorable - calling memories of Serenity's lovesick mechanic Kaylee (Jewel Staite) to mind. But where Kaylee embodied the naive-but-plucky girl viewers either knew or were, both Fitz and Simmons lack any real dimension, or the implication that they have a life outside of their laboratory; any desire to converse beyond their mission-relevant banter.
It's hard to say if the ABC/Disney audience and tone is to blame for characters that fit so completely into existing stereotypes (most likely), but the lack of any tangible depth or quirk means the cast can't be relatable or realistic in any sense - so to endear them to audiences, they have to be funny/goofy/silly/hilariously in over their heads.
Which brings about Agents of S.H.I.E.L.D.'s most-cited problem: this wisecracking, delightfully unprofessional and out-of-their-depths strike team is a complete departure from the S.H.I.E.L.D. Marvel took four films to establish. An organization that now turns to bloggers and social media experts for new recruits.
Firefly's Kaylee might be sweet enough to make your teeth ache, but nobody could bring a broken machine to life like she could (she was able to see the importance in any random gadget - and person... hey, that right there is character development!). Wash (Alan Tudyk) was a pilot whose talents were never questioned, and whose moral compass was often injected into morally grey dilemmas. And even Jayne (Adam Baldwin), the crew's muscle, was many things, but stupid wasn't one of them. In many cases, his unsentimental demeanor produced the most practical solution.
But then, each of those characters had something that is lacking from the characters of AoS: dignity. By making each character an expert in their own right, the mutual respect that permeated the crew of the Serenity meant every voice was valued. Ward or Coulson insult, attack or simply dismiss Fitzsimmons - the only cast even hinting at character depth - on a weekly basis, insisting they 'stay in their lab.' And don't get us started on 'Skye' (Chloe Bennet).
The respect and expertise handed to every Firefly character meant all voices were welcome, with each scene letting characters show their personality. No respect among the cast of AoS means characters' opinions aren't valued outside of their own specialties (if then), leaving the plot to drive all of the events. And the truth is: nobody is watching procedurals just to see the mystery solved.