The mythology has been run into the ground, each week Agents of Shield plays around in the same playground and fans get more exposition than they ever wanted or can handle about the McGuffins from the films.
There can never be a payoff now because just like Lost they are making it up as they go and they have a financial incentive to keep the franchises going forever, recasting leads when they can't afford to re-hire the actors or they want out, and they will inevitably fall into the same traps that the comic books themselves created and fell into.
I'm sorry Bill but I disagree with nearly all of that.
I've watched every episode of Agents Of SHIELD and, aside from one episode every season where Coulson will make out he lent a weapon or vehicle for someone to use in a movie, they don't "get more exposition than (the fans) ever wanted or can handle about the McGuffins from the films". I'm pretty sure the show has never mentioned Thanos, the gauntlet or the gems which are the main elements of the overaching storyline. At most, they've fleshed out the aliens involved in The Avengers and that's it.
I'm also not sure you can make something up as you go along if you're following comic book storylines that have been in place for decades.
I also don't think "alien wants gems for his gauntlet" is overly-complicated as a storyline but maybe that's just me.