It could do with a little nerfing and there have been a couple of matches where I played on the zombie side where seemingly every person on the other side were playing as Rose but I don't think it's crazy bad.
I read elsewhere someone had moved on from Rose into the good old peashooter, because they found their stats better on the peashooter.
It's due a free update soon which amongst other things will do some balance changes and some more maps, old ones too, which will be good fun.
On the plant side I still prefer playing either sunflower or cactus anyway, I got pretty good as a sniping cunt on the first game.