Fanatic is one of my favorite heroes. I can go all day with the tactics that are my favorite and the stories of high-risk, high-reward gameplay, but I'll keep this simple.
Fanatic has a deck full of super powerful cards. No one else can really match Wrathful Retribution, End of Days, Aegis, Divine Focus, Final Dive or Zealous offense. However, the cards don't tend to work well together, so she ends up pretty balanced.
My strategy with her is a full on assault, where I give no heed to my HP and just fly into battle swinging. Zealous offense is one of my favorite cards in the whole game, and teamed with Absolute Zero's sub-zero atmosphere can ruin any minion based villains day.
I like getting Martyr into play early, esp. since it works so well with Zealous Offense (sometimes you can't deal villains 3 damage because of heavy reduction, but damage dealt to yourself counts as damage dealt, so 3 to myself and 1 to a villain counts as 4 dealt, and keeps Zealous Offense in play)
I disagree with how Envisioner sees her, I see her as a true believer, unafraid to get hurt or die for her cause of ridding the world of evil. She gains power by not being concerned for her own fate, she would gladly lay down her life for her friends, or her cause.
One of the ways to ensure you are doing the right things is to look at the overall HP that will change, if doing a full on Martyr (5 to self) will help bring about the destruction of a target that will deal 2 damage to each hero (6-10 damage) then it is the right choice. Divine Sacrifice and Aegis of Resurection is another combo that won us a match. One match two of Omni's EPE's came out in the same round. We were able to knock one down, but the second was going to wreck us. I had Aegis in play and 17hp, so I used divine Sacrifice on it, it dropped me to 3hp, then 0, where Aegis restored me to 10hp, and the third incapped me. The other two heroes won the game, but wouldn't have if that EPE had been allowed to thit them.
That is Fanatic to me, the one hero that is most willing to die for the win. She loves to go down fighting, and it is rare that a villain can survive her.