Initial impression on Ana from a few games in QP which are far from being good representation as most teams had 3-4 Ana, 2-3 D'Va and McCrees.
She has zero mobility, no wall climbing, no hooks like widowmaker, no speed boost or ability to fly away like Mercy. Having no ability to get into hard to get sniping spot, and no ability to escape combat if in close quarters makes her extremely vulnerable.
Her sniping healing hitbox seems to be very generous, as I didn't find it all that hard to hit my teammates to heal them. She doesn't seem to be able to do headshots.
The sleep dart is pretty good, interrupted a McCree High Noon with it.
It's a mez that last 6 seconds if the player isn't hit which is probably gonna end up useful to disable someone during a push, or resisting one.
The AOE heal is fairly small, but heals for a lot so it's feels pretty good on some maps, some of KotH where everyone is crowded on point, I guess it could be pretty big deal.
Her Ultimate is extremely powerful, putting on charging Reinhardt essentially makes him clears the area he charges in even without his ultimate, he does lot of damage, gets damage reduction, and moves very fast. I've seen a few charge a point, and clear it by themselves, as no one can escape his hammer swings.
She's lot of fun, but will be one of the high skill hero, she's not gonna be the easiest hero to play.