Let's talk about the Marvel cartoons produced in the last 15 years or so. My opinion is that series such as X-Men: Evolution (2000-2003), Fantastic Four: World's Greatest Heroes (2006-2007), Wolverine and the X-Men (2009), and Avengers: Earth's Mightiest Heroes (2010-2013) are very fine works of art, and I've watched them multiple times with my (non-superhero loving) girlfriend to great mutual enjoyment. However, from what I can tell more recent series have "jumped the shark" and have become barely watchable. It's not completely definitive that Disney is the one to blame, but it does match up pretty closely with series that are entirely developed and produced post-buyout.
The change seems pretty clear to me, and I can see it in both the one-season cutoff to the Wolverine show, and the distinct tonal change to the Avengers show in its second season. Wolverine and the X-Men was perhaps the zenith of Marvel TV production, having evolved a very mature sensibility and style, presenting an unrelentingly tense, and frequently terrifying look at a nigh-dystopian present and future. Avengers: Earth's Mightiest Heroes, while having a more cartoonish art style, had very textured characterizations, and an ingenious season-long plot hook, which I found to be extremely satisfying (and I wrote about here).
More recent cartoons (Ultimate Spider-Man, Avengers Assemble, Hulk and the Agents of SMASH) suffer from a number of self-evident problems. One is that some directive has gone out to explicitly skew them towards a younger audience; gone are the tense themes from the earlier X-Men series, for example. Second, and related, is that some requirement has been put forward to make them "funny" in the most juvenile fashion possible: it seems like every episode requires one or two slapstick moments or really stupid, forced jokes. (Examples: mini-Spider-Man asides to the audience in the fashion of Family Guy, Hulk mugging for the camera in a reality-show "private cam" recording device, Iron Man announcing that he's erased Dr. Doom's video streaming queue, etc.). Third, the shows seem to have become nearly wall-to-wall mindless violent action sequences for the entirety of the episodes (some of the best scenes from the old Avengers show were the complicated evolving relationship between Clint and Natasha, or Steve trying to give Tony boxing tips; no more of that). Generally the characters seem a lot dumber, either because that's supposed to be funny or because the writers are lazier about caring for forced or holey plot points.
If you watch both of those videos above that I found at random in the last day or so, for about 2 minutes or so each, you'll notice that both of them feature giant green booger jokes. Maybe that was actually a requirement from the executive offices, I don't know.
Another problem, most evident in the Avengers Assemble show, is that the old show was terminated and the new show produced in order to align the property with the current Marvel movies being produced. Specifically: the character designs were redrawn to make the characters look exactly like they do in the movies (the cartoon Captain America now looks exactly like Chris Evans, Hawkeye like Jeremy Renner, etc.). But this is a fool's errand, because the the cartoons will constantly be playing catch-up to the movies in this regard. Consider: A cartoon series produces around 20 episodes or so per year, while a movie franchise puts out one production every two years or so; therefore the cartoon needs to present about 40 times as many heroes and villains over its run. Granted that movie producers are given free reign (and encouragement?) to totally re-design any character from the ground up, they will without exception be different from the cartoon, and thus leave the cartoon once again out-of-synch with the movie property. A great example of this is the Avengers Assemble inclusion of the Falcon as a primary team member; while all the other members look identical to their recent movie appearances, the Captain America movie coming out next year has used the Falcon character, and of course totally redesigned him, leaving the cartoon distractingly out-of-synch in this regard. But that would go for any hero or villain covered by the cartoon that a movie later opts to use. Really better to let the properties evolve naturally in their own universes, as these kind of misalignments are inevitable, and only highlighted when the other roles are freakishly duplicated.
So it seems like to me, the "golden age" of the animated Marvel TV show has come to a close, in light of Disney looking like it's forcing an attempt at a much younger audience, and requiring that the shows be an appendage to the enormous movie franchise that they currently have going. (Which is a loss in the sense that I think that the recent cartoon shows had much more satisfying writing and character development; not being allowed to truly take advantage of the longer-form medium is a real shame.)
A final, corollary point is how this development again proves the lie to late-era D&D and Star Wars apologists (etc.) over whether our vision is clouded by mere age and nostalgia. Once again we can easily perceive a compelling and exciting piece of storytelling (like Wolverine and the X-Men or Avengers: Earth's Mightiest Heroes), even when we are well into our adult years, and note the disaster that occurs when the property is taken over by marketing interests who want to change its pitch to an audience of the youngest children at all costs.