1) Like Ben said, it looks like this will definitely add a lot of power to theme decks, though I'm not sure they really needed them.
2) The resource returning side effects of Unliving, Soldier, Mage, and Undead have definitely substantially increased their power, when they were solid keywords to build a deck around in the first place. Alliance definitely had a nice side effect, but not really enough cards or synergies to build a deck around yet, IMO.
3) I'm mostly enjoying making hybrid theme decks.
As for the flare attack on a common, I like it so far, but maybe that's mostly because I've been making good use of it, and haven't had anyone use it against me. The thing about it though is it doesn't really give any benefit to the person using it (except for the few burning cards that depend on burning cards in hand), it's mostly just useful to screw up an opponent's hand, especially if they're relying on mob tactics that certain keywords (undead) lend themselves to.