Personally I don't like the art much, but it's clear enough to see what's going on so at least it doesn't impede understanding of the story. The story itself is fairly weak; the card games, and the reasons to have all these card battles, quickly become repetitive and although the author clearly did a lot of research into mythology, the way the game is played seems unrealistic because she's obviously making it up as she goes along to suit the needs of the story. All these hardcore Chaos players get thrashed by a girl who knows virtually nothing about the game. They're all shown to be obsessed with gaining powerful cards, such that they completely overlook important properties of "weak" cards that can completely turn the tide of a game just when it seems like it's impossible for the loser to make a comeback. The card game just wouldn't function in real life like that, real card game champions would not play like that, and I think that's why if you're a card game buff looking for a story relating to your hobby or just someone looking for a shoujo with a twist, this is definitely not the manga for you. It's nice to see something a bit original rather than just a high school shoujo romance but I don't think the card game portion of the manga really works.
Aside from that, my main criticism would be that Manami is an incredibly annoying character. She bursts into tears all the time, she comes across as very one-dimensional and she's always relying on other characters to help her or protect her. People who are introduced as villains-of-the-chapter change their minds about hating her within a few pages just because she "respects the cards", she "really loves the game" or she "teaches" them they've been playing the game without any "heart" or something like that, and then they all worship at her feet. In my experience, if you burst onto the scene of a new game and try to play in such a soppy and emotionally-charged way, the experienced players will just beat you into the ground and then mock you. The whole message of the manga is really cheesy and most of her feelings about Chaos, the inspiration she spreads and her experiences with prophetic dreams and Sahgan's world "within her" is really hard to take seriously because it's chock full of narm.
However, there is a reason I read this till the end and that's because there's a fairly intriguing love triangle. The only remotely interesting character in the entire manga is Araki, who's one of those mysterious playboy bishounen types, and gets probably the only decent character development in the whole story. I think he's the only good reason to keep reading this manga and if shoujo love triangles are like crack to you then you might be able to overlook the many flaws and find this manga tolerable. If not, this is not the manga for you.