I actually liked Iron Man 3 a lot, the super dry and sarcastic tone was a perfect fit for the character. Obviously there was some silly stuff but I think thematically it worked very well, it also shows us that Tony himself is the hero whether he has the suit or not. It's also the closest thing we get to a Vision origin story considering how important Jarvis is to the film. If you look at the Iron Man standalone films as a trilogy it works well as a conclusion to Tony's original arc while setting up the MCU's big picture arc. Ultron was a flawed movie but necessary for Civil War, and Ultron doesn't work without Iron Man 3. The worst thing about IM3 was the ending, Pepper going rage mode while Guy Pearce screams the thesis of the movie at the audience through bad CGI does a great job and ruining the rest of the movie.
It makes sense if you think about the Iron Man movies and villains it like A Christmas Carol.
Iron Man - The ghosts of Tony's past. Ruthless, selfish, uncaring, he would have turned into Obidiah had he not been taken hostage. In many ways Obidiah is a dark reflection of Howard Stark, whose shadow still looms over Tony at the time of this film. Tony can't become a hero until he deals with that baggage.
Iron Man 2 - The ghost of Tony's present. Tony has opened Pandora's box with superhero/ark reactor tech. Vanko is just as smart as him and Hammer is just as reckless as him. Tony needs to learn that he no longer has a monopoly on power and therefore he can't just act for himself anymore. Other people have the ability to check him now (other heroes, villains, or SHIELD) so he needs to get his shit together and finally grow up.
Iron Man 3 - The ghost of Tony's future. He has to decide what kind of hero he's going to be, will he hide in the shadows with no accountability or work cooperatively for the greater good? Killian is a shadow villain whereas Tony embraces the attention that comes with his position, and learns he has to accept the consequences of that even if it puts those he loves in harms way. This is his motivation for creating Ultron/Vision, in his mind it's a necessary evil.
The three of these work together to give us reasons why Ultron/Civil War/Infinity War Tony is the way he is. Tony and Steve and the most highly motivated characters in the MCU which is why they're always at odds, and his experience in Avengers 2012 shows us why he's so obsessed with Thanos. Thanos has Tony's drive, intelligence, resourcefulness, and recklessness, but lacks Tony's compassion. Tony will gladly sacrifice himself whereas Thanos will sacrifice everyone BUT himself.
Thanos is such a great villain because he brings out the worst in our three biggest heroes. Thor is arrogant and thinks he cannot possibly lose because of his destiny. Cap was quite literally born for war and runs headfirst into conflict looking to defend the helpless. Tony is driven to the point of obsession because for as smart as he is, he doesn't have an answer for Thanos. Thanos is the worst case scenario for all of them. It's amazing long term writing and none of it would work without the silly stuff in the bad standalone movies which look bad in isolation but make sense in the broader context.
