Don't underestimate the power of over saturation to bog down on the mind. You're talking about the acting in Avengers as though it was child's play, yes TDK was a serious film and I credit everyone's acting in it, it was top notch, but just cause those characters were written more seriously or in a more quirky manner does not mean it took more to portray them than it did to portray characters in Avengers.
The way Cap is the most subdued soldier and most respectful gentleman at all times, where you can hear in someones tone and sentence structure that they are just raised to be completely respectful of others and are from an entirely different era, that's not a walk in the park cause it requires a more subtle finesse.
Even characters like Loki and Thor, Loki especially there's a special brand of maniac that Tom Hiddleston plays, his villain maybe just as evil as or more evil than Joker but he plays a character who like a child just wants to be acknowledged and respected, most of his acting he does with his eyes, the way he looks at different people differently. His disrespect for humanity shows a certain glare of self importance as well as a general disregard for their ability, whereas when he's around Thor, it's more of a hatred and fear emotion, born in jealousy.
If you're not paying attention cause you're dismissing it as b grade popcorn movie stuff, then of course you're going to say it's not worth writing home about, Tony stark for instance has to be arrogant, smart, funny and always thinking, so while he's popping off one liners and being silly, he's also calculating, you ever notice how he's eyes barely ever stop shifting around like he's trying to figure something out the whole time?
I'm just saying, we've already discussed how the films have very different tones so it's not even a good comparison to say no one here will get an oscar so it's not a better movie, and since when did oscars become something we depended on to decide what is a more enjoyable movie? these are comic book films, try as you may to want to believe that the Batman films are something more, they are still comic book based films, yes the stories have more weight but that's because their realism lives in the bleakness of our world, it's not any harder to make a gripping film than it is to make a lengthy action film with comedy in it and still have it be something that might make fans even a bit emotional... have you ever tried to act like you were talking to someone who isn't there? imagine that in movies with a lot of CGI, it's not easy, look at how bland and monotone the star wars films are because of it, because the director didn't take the time or the care to try and get his characters to seem more involved, it's not a cakewalk, it's not "come to set, crack a few jokes, go home get paid."
But like I said, the batman films are great, Heath Ledger in the dark knight is superb, but one or 5 actors don't make a whole product. look at Avengers, all those actors doing their thing and some people will still say it was boring when there wasn't any action on screen. it's not just the actors, it's the writing, it's the directing, it's the sets, the locations, the whole product, so yes The Dark Knight had a lot of great things, but until people see The Avengers, it is an ignorant statement that some make to say "I know TDK is better"
It's like saying I've never had vanilla ice cream, but I know chocolate is better. they are 2 different flavors, how will you know which you actually like more if you don't give both a chance?