In an effort to get people to understand just what on earth it is that they really believe, Christians gave god certain attributes. Once you give a god attributes, it then becomes critique-able. For example most Christians believe that god is omniscient, which is perhaps one of the most problematic of the Omni's. One of the difficult problems to wrap your mind around when dealing with omniscience is the following argument.
Omniscient beings do not have free will.
God is omniscient.
Ergo, god does not have free will.
If that is a bit hard to grasp, I'll try and explain it. If a being is omniscient, it literally knows everything, so it would know the decisions it would make in the future before it made them. This creates a confusing dichotomy, as if you know what you're going to do at every moment in the future it is hard to definitively say when you made the choice to enact that decision.
Once you add another popular attribute into the picture it becomes even more paradoxical. Lets say that god was omnipotent as well as omniscient. Omnipotent literally means all powerful, so an omnipotent being should be able to do anything. Would an omnipotent being that knows what decisions it was going to make in the future have the power to change them? If not, it is not omnipotent. If so, it is not omniscient.
Enough of the brain-melters....
The moral implications of omniscience in particular are also troublesome for Christianity. If god created Satan knowing that he would become "the devil", then it could be said that god created the devil expressly for that purpose, to be evil. The same could be said about individual people, for example Adolf Hitler.. If it was true that god had foresight of all the events of humanity before he "created", he is directly responsible for absolutely everything. Just trying to think about the implications of omnipotence and omniscience in regards to creationism is just giving me a headache now, so I'll leave it there.