This is going to sound very wrong, but I think Jane Levy is too pretty for Iris. I've always envisioned Iris as being a girl-next-door type who's the kind of girl who normally wouldn't stand out in a crowd, but once you're into her, you discover she was beautiful all along.
As sappy as that sounds, that's how her and Barry's relationship was pretty much portrayed. She's not like Lois Lane with men fawning over her. That's part of what I like about her character so much.
Jane is too model-like. Emma Watson doesn't seem right to me either. Her chemistry with Ezra in Perks was fun, but it was too brother-sistery for me to wrap my head around them in a romantic relationship. Funnily enough, Aaron and Elizabeth are going to go through the opposite transition in Avengers AOU after Godzilla.
Emily Osment isn't a bad choice. Still prefer Shailene, but Emily could use another big movie to get her out in the public eye again. She's a decent actress.