Appatently I never reviewed the game before, so here I go.
This game easily falls into the top five CCGs on the site. In terms of Strategy games, probably within the top twenty or so.
I encourage people reading this to open the swf file in its own tab. That way, you get a larger screen and can see the cards and their descriptions without having to click on them.
In terms of praise, probably the single most innovative feature of the game is insanity. I have never seen anything like it in a CCG before or since, and provides another layer of strategy.
My only complaints are minor. There are only 36 cards in the entire game. Contrast this with something like HD: Xyth which has over 100 cards per race, and with nine(ish) races this comes to about 1000 cards in the whole game.
Card balance. Yog-Sothoth, which you receive somewhere around level 25, allows you to kill a high-sanity medium-health player in one hit. The AI seems to love using this card. Quite a few attack cards ignore invulnerability (3/36) and defense (5/36). Perhaps invulnerability should've been named "spell invulnerability" or something, considering that's what it really is.
A few minor gameplay issues. Your creatures only attack in retaliation of your opponent's attacks. Almost all creatures' attacks can be blocked with just a little defense, and possibly with your own creature (trivial even in lower levels). In addition to making creatures unimportant, the effect of this is that your creatures just sit around twiddling their thumbs almost the entire match, which is quite a shame.
Nevertheless, the game is perfectly addicting. It's a shame they don't make games like this anymore.