Given that God is, the remaining question is how can we know more about Him other than that He defines reality. The answer is experiential knowledge. While many beliefs about God have been put forth throughout history, it is our experience of Him that truly validates any knowledge about Him we may have. This is similar to many people forming many different opinions regarding a certain type of food, but only those who have actually eaten it are really qualified to comment.
This is the primary reason I find theological debate mostly useless—it is done by those who have not experienced God. Those who deny God's existence are simply fools. If they were honest with themselves, they would admit that they merely doubt God's existence because they have not yet had sufficient evidence to convince them. On a deeper level, I would suggest that these people actually hope that God doesn't exist and have in fact come across quite a bit of evidence that they would like to ignore. But those who engage in more "substantial" theological debates about God fall into two camps—those who believe in Him and those who don't. There is not much difference between them. The knowledge that forms their debate is based mainly on belief, consideration of the evidence for various attributes or actions of God. However, most of those involved in such debates tend to emphasize narrow domains of evidence that support their hopes about who God is and what He does. Being the foundation and essence of reality, God is unsearchably deep. Therefore, avoiding an ever deepening understanding of Him causes one to miss much and form a warped perspective of God.
Experience is the antidote. Once one has experienced God, they realize that what they have touched is unsearchably deep, indescribably rich, and extends infinitely beyond what they can comprehend. Yet this experience brings with it knowledge of God that both satisfies the recipient while at the same time encouraging them to go deeper. Thus the only commentary on who God is and what He does that I trust is that put forth by those who have experienced God and who encourage others to do so. In fact, these people need not debate much. They know that if those who would argue with them would simply experience God in even the most minuscule way, they would have a revolutionary change in their knowledge of reality.
This experience supports all other means of knowledge as well. The beliefs of those who experience God are more substantial, being based on compelling evidence (namely the Bible) that matches their experience. Some aspects of God's person and work even reveal themselves to be self-evident, becoming facts to those who experience God. And the hope held by those who experience God is more firm, more real, and more obtainable than any other earthly hope. What a thing it is that man can experience God.