The problem with Ana right now, and probably for the next few days is that people don't know how to play her, or play with her on your team.
She's not an easy character to play. She has one of the highest skill cap in the game.
The first issue is people are not used to having a 2 healers support team. They think she can solo heal, which she can under certain circumstances but generally it's not a good idea to have her solo heal.
The second issue is people think she is a sniper and try to play her like Widowmaker, she doesn't play play like that at all. She's really a midrange hero that can snipe a little. Most of you shooting will be unscoped from the hip. She's awesome at sniping a friendly Rein that just charged into a group of enemies...and if you're good at throwing your grenade that has essentially unlimited range, you throw it in the group he just charged, they get no heals, and he gets a bonus to heal received that you're doing from a distance sniping...and if you miss him, you're probably hitting an enemy near him.
The third issue, is getting good at positioning yourself to get a good line of sight to all of your allies. You have to be careful...the hitbox for the heals is HUGE, and you will often get your heals intercepted by an ally standing between you and your target, or have an ally walk in front of you intercepting your heal intended for someone else. That is most likely the most annoying thing about playing Ana.
The fourth issue is the sleep dart. First don't waste it sleeping random enemies. It has a long cooldown, and it's your only escape ability. So make sure you use it carefully. Second, try to communicate that you're going to sleep a target when you can so your team doesn't break the sleep...which they always do anyways.
You can sleep a dragonblading Genji, but if he is woken right away, he is still under the effect of his ultimate and will slice everyone apart, let him sleep off.
She's tons of fun to play once you and your team get used to her. I loved her on the PTR, I found last night extremely frustrating both playing her and playing with her on my team as people are simply not used to her...mostly refusing to get a second healer and asking her to switch because she sucks.
Same happens with Zenyatta, he's not great at solo heals...people are still asking others to switch off him to a Mercy or Lucio rather than have another healer in the group.
It looks like the 2 healers meta from PTR hasn't reached live server yet.