I’d like to make Zarya speak Russian and remove her holywood russian accent. I’d also add that Zarya voice should sound more powerful, but needs soft voice lines too.
Sigma. Yes, ikr, Sigma VA did an incredible job. It’s writers fault. They didn’t make him feel insane. He sounds like a quirky grandpa with PhD that refuses to retire. I’d like him to sound more mad or violent at times. He also could use more philosophical lines, but that’s just me.
Mercy. Mercy just needs to sound softer (just like in Russian) and get rid of fake accent. Writers massacred this character as well, and she doesn’t seem as angel, but as bottom hypocrite. Like, her kill lines reveal what a basic 
she is.
Echo. I think they did a terrible job with Echo. Her voice lines are generic and doesn’t reveal anything about her. I think it would be really awesome if she was more terrifying, because, damn, robot that can copy anyone should sound cooler. She could discuss different paths of adaptation, or just copy and paste other heroes lines. There’s a breach between Echo’s personality and personality of a creature she copies, and I think, Echo should have abandon her security programs and become more empathetic and flexible to a person she copies. I mean, that flexible that she would talk to Talon members as to close friends.
Why would she abandon security though? Easy answer. Officially, her project is under quarantine and overwatch is illegal. To join them, she needs to adapt to new rules.
We need Hawaiian BOB skin
~ decomposing