Kay, so here's my take on Arena 12: I hardly reached it. I was faced by barely surviving A12 players every time I reach to a 1-win distance to Arena 12, and I gotta say, those players are violently good, that I wasn't able to do much.
So, my first experience was more of what characters in Pokemon games say about the elite four and champion, except this time, I literally mean it when I say that the people up there are incredibly skilled.
I even decided to make myself some better decks that at least have some levels available to do for when I go up the ladder, I don't have to go with Level 11/9/6/2 cards.
How was your experience, or what do you expect? Because, I seriously suggest you take a look at your deck several times before going up there.