As Avengers: Age Of Ultron has been in cinemas for a while now and afforded the fans who weren't preposterously disappointed by it a chance of multiple viewings (the way it deserves to be enjoyed), a lot of picking apart has already been done. There are questions for the future of the MCU, there are plot-holes and there are even suggestions that the whole thing is a sign of an impending creative apocalypse.
And of course there's also been a lot written about the film's Easter Eggs, in-jokes and references, which were consciously - and unjustly, to a degree - played down by the director.
Joss Whedon may have under-played the presence of Easter Eggs, but expecting no references in any comic book movie is like expecting Quentin Tarantino to refrain from the same thing. Yes, there were fewer, but Whedon's admission was more about not trying to outdo the other films to the cost of his narratively-stacked film - something he was probably losing a lot of sleep over considering his battles with the producers.
If you look hard enough and know your comic book lore, there are more than enough fan-baiting details and references to delight even the most cynical of audience members.