These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
All Hail the King reveals that there is an actual Mandarin who runs the Ten Rings organization that kidnapped Tony in the first Iron Man movie, and he is very displeased with what Trevor Slattery did to his image.
Broken Base: Some fans were displeased by the reveal that All Hail the King would star Trevor Slattery. However, the short reveals that Trev's earned the ire of the real Mandarin (who apparently very much exists), which has been a very pleasant surprise indeed for some detractors.
Breakout Character: Two, Agent Coulson and Peggy Carter. Their growing popularity was tested out with these shorts, and each successfully springboarded them into receiving their own TV show.
Growing the Beard: The first short comprises of nothing more than a clip from The Incredible Hulk bookended by clips of S.H.I.E.L.D. agents conversing at a table. It's clear the budget wasn't high on this one. The following shorts rely more heavily on original footage, display special effects, and boast more interesting plotlines. Now Marvel uses them to test out side characters and seeing if they're received well enough to make the jump to their own show or film.
In addition, Sitwell's legendary patsy act referenced in The Consultant. So good it fooled Coulson, S.H.I.E.L.D. and the entire audience into believing he was a loyal fellow agent rather than a HYDRA mole.
Ho Yay: Justin Hammer at the end of All Hail The King seems to have a prison butt buddy that follows his every move and order without a word. His talk about Tony Stark and his jealousy of him also questions his orientation.
One-Scene Wonder: Herman in All Hail The King, who is Trevor's loyal Black Best Friend and manages to fight off Jackson for more than ten seconds before getting killed by him.
Pandering to the Base: All Hail The King gets this criticism from some; specifically, those who thought The Reveal about the Mandarin in Iron Man 3 didn't ruin everything. Said viewers were OK with that reveal, and felt that adding this extra detail which probably won't get any further development (see below) was just catering to an unnecessarily-incensed fanbase.
They Wasted a Perfectly Good Plot: One common complaint about All Hail The King from those who likedThe Reveal is that the true Mandarin and his vengeance for Trevor's mockery of him possibly won't receive any followup.