Okay, so I finally had some time to play a few matches.
My overall feeling is that this is a very nice expansion. So far I noticed a huge deck variety in ranked, though I should mention I'm still in Silver, so the meta is not that shaped yet. I think the games required more thought about positioning with respect to the Ancient Bonds times. I didn't see any egregiously broken card, but there are many strong, interesting cards to add to pre-existing decks. I find Thunderhorn particularly nice, because it really forces one to think how to deal with it without losing the board or screwing up positioning.
My only concern is that, if a few of the old cards are not nerfed, we may end up having balancing troubles again. Now people are testing the new cards, but at some point someone will find the best decks to play with and they will likely include a few of the existing broken cards. So I'm having fun for now, let's hope the developers will be quick at addressing the problematic interactions which will pop up for sure!