Fantastic Game
Well done! Love the art and card choices, and the challenge mode is a great addition. I am a big fan of Lovecraft and the Cthulhu Mythos, and have really enjoyed both of these games, keep 'em coming.
Anyway, here's my two cents:
I love the fact that insanity plays such a role in the game, and I really like the random effects of going insane. However, the effects of insanity seem to be a bit off.
The Megalomania effect is perfect. More power while your life decreases works nicely and is great for strategy.
Xenophobia on the other hand doesn't seem to be too much of a hindrance since the monsters are singular, and can only counter-attack.
Schizophrenia just seems to negate a lot of choices, and really just makes a lot of cards useless. Doesn't really hurt the player, but just makes a lot of cards dead.
Agoraphobia is pretty interesting, but I think that when someone suffers this effect, the other cards should be face down.
In my opinion, going insane should carry a 50/50 chance of instant death for either the player or opponent.
It would be incentive to stay away from going insane except in a last resort.
Also, it'd be great to see more than one summoned monster available to attack at one time, and I think that the player should lose sanity for each round that he has one or more summoned monsters in play. (1 Monster -1, Two Monsters -2, Three Monsters -4, Four Monsters -8, etc.)
It would also be interesting if the monsters that were summoned had a chance to overtake the creator. After all, if you summoned Cthulhu, how likely is it that he'd obey your every beck and whim?
Also, it'd be pretty neat to be able to choose an archetype as you started, whose stats would increase each level accordingly. For instance:
Professor: (Higher sanity / Lower Life)
Detective: (Higher Life / Lower Sanity)
Occultist: (Greater magic bonuses / Special Insanity Effect)
Anyway, great game, it a lot of fun. Just make sure to include Pickman next time.