I just finished the challenge mode ; took me all afternoon.
Like others said, it's kinda repetitive after a while but it's not boring.
The gameplay mechanics are cool and effective.
Art is uneven - the three "gun" cards are... well, let's say it reminds me the art of a five-years old I know. On the contrary, I like the shoggoth and R'lyeh.
My major problems are with the challenges where your Life start VERY low - #13 and especially 15, without Elder Defense. At Life 5, a third of the cards can one-shot you... So playing those challenges is mostly dumb luck, no strategy. It makes the challenge #15 the most difficult to achieve.
Two suggestions :
- a "story-mode" allowing to retry the battles in the normal game ;
- high-level cards who give more taint : when you start with 50 Life, losing 1, 2 or 3 Life per turn is nothing, especially with the various cards who remove it.
Last, a question : is there any relation between your game and one called "Maganic wars" ? They seem very similar except in their theme - Maganic was purely fantasy-style.