So played a few hours last night on my alt account, didn't want to have to deal with deranking while people figure out how to play Orisa.
She was in a lot of games, either on my side, or the other team's side or both. I didn't play her personally.
Initial impression is that she's not very impactful like no game were really won or lost because of her presence, although I would say she is probably on the weak side, that might be due to people not knowing how to play her properly yet.
She's very easy to kill when not behind her barrier, she's very slow and doesn't do much damage. I think she might end up being one of the worse 1v1 in the game...not just tanks, but of any heroes.
Her ultimate is extremely powerful though...If used properly on either defense or offense it almost guarantees a win. The thing is that it doesn't really require much coordination, just put it down...and everyone does so much damage that it will overwhelm the other team very fast...no need to combo it with anything. I'm pretty sure it will be nerfed hard at some point.
It's a small sample, and not me playing her either...but if she's not viable...she's close and will require minor tweaks...her kit seems solid.
On a different note, I was on Mei, and killed 5 people during my Ultimate while essentially not missing a single headshot. Got play of the game, and was told nice aimbotting which I will take as a compliment.
In a different game, a player said "Whoever was playing Mei...fuck you.", to which a second player agreed with. I also took that as a compliment.
Mei is now by far my favorite character to play, and probably my best. She is just so much fun to play, so many ways to impact the game...her ultimate, or just good wall placement to break/split a push...or stop ultimates with a wall. That's not even counting just freezing someone and shooting them in the face point blank and going "Sorry, sorry, sorry".