What kind of cruel god

You should understand that this movie is fictional, and it was obviously financed by non-christian people, most probably to emotionally manipulate people (like you were) into thinking that God was cruel. It's you who should ask yourself why.

You can read the Bible, to see if there was a recorded case of God's Spirit possessing unwilling persons.
According to the Bible, that woman was most likely possessed by an evil spirit, who was torturing her; she was an atheist, and God doesn't force somebody to believe, nor does He possess the bodies of unbelievers.

Anyway this movie is an example of blasphemy, an unforgivable sin, in this case attributing devil's work to God:
http://biblia.com/bible/esv/Mark%203.22-30

See examples of evil spirit possession described in Bible.

http://www.biblegateway.com/passage/?search=Mark%205:1-20&version= NKJV
http://www.biblegateway.com/passage/?search=mark%209:14-29&version =NKJV

"Would make its most devoit followers experience such pains for no reason whatsoever?"

Before you ask "What kind of cruel god", why not ask - "Is there - or was there ever - a god?"

As for the bible, isn't it a culled and shuffled collection of old campfire stories? Granted some of them are pretty nifty, with some historical reference, and who wouldn't want to believe in eternal life? (what a great enlistment gimmick), but com'n kids.

But lets say, though there is absolutely no scientific proof, that there is / was a god; a jealous god; a god that tests his/her "children" with war, pestilence and disease (cancer anyone?) . . . or how about those folks that love to rape and murder children? Thanks god; I suppose there is a special reward for those children too (were they being "tested"? or was their unspeakable torment for the benefit of their parents - you know - a "test"?).

Sorry, but in my opinion, there are no gods - other than the mythological, such as: Amun Ra, Shiva, Zeus, Ahura Mazda, Thor, Amaterasu, or Yahweh.

Man was not created by any of the gods, but man has created many gods.

I love fantasy and good story telling, whether it be around a campfire or in a movie theater, so keep those myths coming!

The monotheistic god of course. That's why there can not be any (a 3 "O" god: omnipotent, omniscient, and omnibenevolent) as philosophers have proved ad infinitum via the "solution of evil" as I call it (it's only a problem for those who believe in god, it is really a solution, however, for it proves there is no such god of the 3 "O" sort) alone, much less all the other many powerful arguments against "god" (for instance, that "god" is not even a coherent concept since it has many inconsistent or contradictory attributes and an ineffable nature or meaning; and what is incoherent can not be even believed in sanely much less actually exist, like a square circle) starting with Epicurus (despite the pathetic, dishonest, and logically fallacious theodices christian theologians have vainly attempted to convince the gullible and unintelligent masses). Anyone who believes in such a god in spite of the vast amounts of evil/suffering/misery of humans and non human animals is not only intellectually dishonest with themselves (even they truly know it is b.s.) but also a cruel, repugnant, sick and immoral wretch. How dare anyone look upon the suffering in this world and turn around and not only excuse, but also praise and worship, the monster they believe is directly and entirely responsible for it! That takes a very cruel and inhumane heart indeed and a very sick, dishonest, and infantile mind, a believer's heart and mind.