The MCU really lacks an amazing villain, Loki was close but his backstory was nothing special and in The Avengers he was a kind of weak villain. Most criticism i see is quite constructive, and they do give good reasons for why the decoy would have been a better villain. I wasn't really expecting to see him wielding 10 super powered alien rings, but a super terrorist in the vein of Binladen, somebody that would have given Tony a different type of challenge and be after more than just revenge against Iron Man. Don't get me wrong, i did like Killian, and i hope he's alive since there's potencial in him and the best they can do now is move on and work with what they built. And they better make good use of the new Mandarin.