I didn't mention a conspiracy, I do think there's a lower bar for Marvel movies though. Which is what most in here are saying - the work in the previous movies makes the new ones better in some way.
It's sort of like the principle of "goodwill" in the value of a business. It's not just the numbers, but the trust the customer has in the service. In Age of Ultron, this translates to us having warm feelings towards the relationship between the Hulk and Black Widow that goes beyond what we see in that film, but is directly resulting from the affection we have built up for both characters in the preceeding ones. Similarly, when Cap and Stark show down in Civil War, it's growing out of what we've seen in earlier "episodes" - a lot of the motivation and sympathy for the characters is already established, which is how the big Marvel team-up movies are able to get down to business and we care about the characters because we've met them all before. Giving Spider-Man a mentor, given his age and everything, makes perfect dramatic sense. Making that mentor Tony Stark means we don't need to spend time on a secondary character. We know his deal, we can get back to Spidey. If there had been no Iron Man movies then making Iron Man Spidey's mentor would be weird and clunky.
So yes, Age of Ultron leans on the first Avengers, and Civil War leans on lots of stuff, (and one film does it more effectively than the other.)
Justice League has none of that goodwill. It is leaning, awkwardly, on a pile of cinematic shit in one direction, and absolutely nothing in most of the others. I mean, if they'd cast the guy from the TV show as the Flash maybe someone would give a shit about him, but based on what we see in Justice League it's very hard to care. The one solid pillar that JL has is Wonder Woman, and I feel like it misses the boat there, too.
The issue with him making jokes all of the time isn't really anything to do with Affleck though, it's down to Whedon (I assume) forcing them into the movie in places they don't fit because the suits wanted to lighten the whole thing up. I could be wrong but I got the distinct impression during JL that Affleck couldn't give a fuck any more, he knows this whole thing has been a train-wreck and he's not arsed, possibly why he's not directing a standalone thing any more. He felt like a very good fit in BvS, in fact the only thing I didn't like about him in that (Martha business aside) is that we never saw what brought him to that point in his life.
Yes, but you expect an A-list actor to be able to sell a gag, even if it is an awkward fit. I can see why Whedon wanted to lighten the tone, otherwise why bring him on board in the first place, he has to make it funny and he only has Snyder's cast to do it. The Flash is clearly meant to be light relief from the off, but again Snyder has cast someone who can't sell a gag. Having Batman deliver snappy wise-cracks is Whedon all over, and I can see exactly why he attempted it, but when that fails, it really sounds a bum note.
I'm still not sure who to blame for filling JL with Wonder Woman upskirt shots, could easily be either Snyder or Whedon.
And don't forget the new look Amazons in latex sports bras...
I should reiterate that I did not hate Justice League. It was sort of fun for a couple of hours. But the more I think about it, the more there is that just went wrong.