I am not saying he should be portrayed as crazy, mental illness is a real thing that people have. Like Schizophrenia. I am saying that at first in the films (Avengers or Ant Man) he should seem OK, maybe a little unstable, but more or less fine. Then he starts getting worse, and then has a breakdown in which he creates Ultron and uses his own brain waves as a blue print, then he starts taking medication and gets better and back to feeling more normal. (But like someone mentioned, he starts creating Ultron way before his breakdown. But because he uses his brain patterns, and created Ultron, he blames himself for everything Ultron does.) But every so often his character can slip a little, and thats when he can maybe change his identity. Or he can get better and take medication, but still change his identity because he still has low self esteem.
I just think it makes an interesting character. He is a brilliant scientist, a great hero, a good man, but he has serious mental problems that he has to deal with at the same time. It makes him stand out from the other Marvel heroes, and it represents a portion of the audience that has mental issues and shows that there is nothing wrong with them and maybe can help people talk about it. but mostly it makes for an interesting character and film I think. I personally think it makes him more interesting than a simple scientist who made a mistake or an insecure sap.
Much similar to Stark's drinking problem, they could lighten up on his mental illness too. Not make it so intense, like a Beautiful Mind. Perhaps its shown and touched upon and is an issue and he does have a break down, but its not so dark and scary and intense and sad. But I do think he should have mental problems and show him deal with them.