From my experience, I never thought that they ever did any of the villains justice. Loki failed time and time again, Whiplash was decent but his character arc left a lot to be desired. Ronan was the most intriguing one to me, I would like to know more about his history. Malekith was like a galactic Freddy Kruger to me, Darren Cross was just a pissed off intern, Dormammu didn't really have a lot of time for me to know if he was a good villain or not, Ultron could of been a pretty unbeatable foe like in the comics where he replicates himself so he would just have to download himself to other bodies that he's built but that obviously didn't happen. I didn't care for Abomination much and Ego was a bastard so he was a decent villain but met his demise. I want to see more of the Grandmaster though, the MCU shows his weirdness and all, Hela was wicked but was killed during Ragnarok and it was more so of her having daddy issues than wanting power or to rule. Red Skull was a good villain so it was refreshing to see him again even though he's a completely different character at this point. Erik Killmonger was more of an anti-hero who had valid ideologies but I don't think that we'll see the last of him if the MCU is following the comics for him. Vulture, now, this guy was a bad ass. He did the big things on his own and had his minions distribute his illegal arms to the streets.
Now to Thanos. The baddest of the baddest. From all of the teasers on Thanos, until Infinity Wars, one can only speculate how he's going to take down all the heroes in the MCU and did he! His fight with the Hulk in the beginning shows the audience that he's no stranger to handling things on his own and from what Ebony Maw mentioned, he enjoys it. If this guy can scare the Hulk into turning into Bruce after being the Hulk for over two years, then his a formidable foe indeed. Guy even sacrificed the daughter that he truly loves given that he truly doesn't really care about anyone minus Lady Death in the comics.
I'm going to agree 100% on Vulture. I loved the character and Michael Keaton played him to perfection. MCU has gotten a bit of a reputation for not doing good villains, so it was refreshing to see one that was a credible threat and just well done.
I have to disagree a bit on Loki. I have enjoyed the character development of Loki over the several films he was appeared in, but I think the problem is that Loki walks the line between a villian and an anti-hero. He's just ... unprincipled. He is chaos. Which, in the end, is the essence of Loki. Like he says in the very first film: "I was just having a bit of fun, ruining my brother's big day." No deep nefarious plot to take over, just ... misguided mischievousness. Since then he's been a King - and a prisoner, and he feels like he was robbed of his birth-right (which he was) and deserves a throne (which he does not). But he's always fun ... which makes him a great antagonist, if not a great villain.
And that's the MCU key, I think: They have great CHARACTERS. They might not be what we expect or the true essence of what they are 'supposed' to be, but they're still excellent characters and watching them interact is always a lot of fun.
This dove-tails into one of my main problems with the last couple of SW films. The SW characters are NOT great characters. And without great characters you simply cannot sustain a good story.
