I've been playing her a lot on the PTR. I'm probably going to be playing her a lot when it goes live. You'll like the changes - she's just as aggressive as she always was, but this time won't melt. The skill ceiling for her just shot up a couple of stories as there's going to be a lot of strategy as to where you weave your Defensive Matrix into play. Her ult changes are pretty fun too: she doesn't die to her own ult anymore so when you drop it on the point and force people to scatter, you can follow up and force them to fight you or go out of cover to get a face full of explosion.
Zenyatta feels much of the same - still doesn't have the tools to escape when he gets focus-fired, but now at least he can fight back for an extra second or two. His Harmony/Discord orbs are pretty much instant now which makes him very dangerous if he's got sightlines and relative safety. He's hilariously fast with the ult now - got from the bus on Numbani to point A with a second or two on the ult to spare.
Haven't tried Mercy yet, but people were complaining that it feels like her ult takes forever to charge. That's a good thing, honestly. Having it up for
every teamfight wasn't good.
Ana feels like she's going to be a meta changer. She's got enough utility that she'll affect a lot. Big flashy ults are in a lot more danger from the sleep dart. Flankers too - the stun lasts like 6-8 seconds but will break on damage, so if she stuns you with no enemy around to hit you, you're out of the fight for that time. Aggressive tanks are going to be great ult targets: nanoboosted Reinhardts are absolutely terrifying to watch and a common strategy I ran into on the PTR is Rein charges into a point and gets ulted. If this is common, it might be an indirect buff to characters like Mei as CC will be more important than ever. Junkrat and McCree players will get rewarded by more precise stun and trap play. Zenyatta too, as Discord will be useful to burn the nanoboosted target down.
Playwise, she feels like a cross between McCree and Widow. Her left-click is single-shot, but doesn't have the deviation you normally get when firing sniper rifles in games without the scope up. Her scope doesn't have a charge mechanic and she can't headshot. It takes about three shots to kill one of the training bots. She also doesn't seem like she has any assistance with hitboxes so she seems like, if the player is good, she'll carry her team. If the player is bad, she'll be a handicap.