Fun and addicting, but not without problems
There's a very strong social aspect to the game. If you want to get anywhere, you'll need to make use of the forums, of which there are several, for buying, selling, and trading cards. This can be another point of frustration since the lack of an in-game auction or selling system (beyond direct trades between players) makes selling cards tedious and unreliable. At the time of this writing there is some speculation that an auction house might be implemented, but that seems to be mostly wishful thinking.
The last aspect I'll touch on are the events, which are held every few weeks. Generally, you'll need to be a member of an order (for the Holy Wars) or would strongly benefit from being in one for the quest-events. I absolutely love that events give rewards for both individual and order accomplishments, since it really creates an incentive to work toward a larger goal while still benefiting players that perform well even if their order does poorly. Even though their has been some anger by the players over the handling of the most recent couple Holy Wars (because of problems with the first War, another was held only a short while later), in my admittedly limited experience they've been enjoyable and are something I look forward to.
To sum things up:
Pros
-Addicting and engaging
-Rewarding play experience that makes you feel like you're working toward something
-Demands player interaction
-As I mentioned, giving out both individual and order rewards is a spectacular idea
-Got to mention the beautiful art on some of the cards. Game looks great all around
Cons
-You WILL need to work to get started, and unless you're very, very lucky, nothing is going to be handed to you
-There have been complaints about Cygame customer support and their method for dealing with problems
-I've never spent money on the game myself and never intend to, but it seems even the packs you buy give a lot of bad cards
-There are hackers and scammers, but that's to be expected
So give it a go! It's certainly worth trying, and you'll probably find yourself really enjoying it.