I'm not sure you can ever argue convincingly that the original Guardians of the Galaxy villain was well written though. Maybe his motivation was a little clearer, but like a lot of Marvel villains, he was was one of the weaker aspects of the movie.
Best villains are: Loki, Modern-day hydra and ummm....Avengers vs Avengers!
That's funny because I think Loki is an awful villain, oh no, I was never in line to be king as Thor was always the one who was supposed to be king, you treat me great but damn you, I really wanted to be king of an ice planet of blue people with no power.... I'm so mad I'm going to use my super powers to basically be absolutely rubbish despite the ability to make people see whatever I want being so overpowered it's crazy. Honestly I don't even know what Loki's actual powers are, that's how well explained he is, he's a trickster, it's magic? DO the blue people all have magic, if not why does he. Can he only create illusions or can his illusions do damage and if he can make people see whatever he wants and not actually see him, how can he ever be caught... like, ever? He's got the worst reasoning, the least explained abilities to the point I literally don't even know what they are(do his illusions have mass, can his projections cause harm and interact with things, harm things or not?) and he should be basically unbeatable.
Hydra is cheap tacky writing, we beat hydra... oh wait look, they're over there. When they want to... they manage to spot these enterprises, find all these people and take them down but over the past 50 years they couldn't find them at all, every time you cut off one head, another head becomes magically visible and they have tech/knowledge beyond Shield and have had decades to prepare but always get beaten. It's just cheap hack writing and the big hydra bad guys, I wasn't a fan of the red skull but that whole film was weak.
Avengers vs Avengers was more painfully weak crap, bad action sequences, lets keep them from that jet we could just blow up.....wait a second. THe reasoning for the split was weak, the shoving of extra guys into the fight was weak. I mean, you can do that film with the same basic premise but a fight to reach a jet, that is what made the avengers fight each other, that was genuinely pathetic.