I've been really enjoying it. It's easy to drop in just for a game or two, which makes it different than LotR or Magic, in which game takes relatively more time.
I also started by wrecking a whole lot of people, then advanced to a place where folks are about as good (Casual uses an MMR system and the ranks naturally correlate with skill).
It's true that you start with relatively few cards, but the progress doesn't feel too slow and getting new cards is satisfying. A couple of the more popular streamers have also taken free to play/mostly basic decks all the way through the competitive ladder, so while you can't play every deck without devoting time or money to collecting you can definitely play with the best.