Omniscience is completely inconsistent with experiencing any of the "surprise" emotions, be it regret, dismay, remorse, delight, etc. You cannot sneak up and surprise or startle an omniscient being, as He already knows all, including future outcomes and events.
(In fact, a moment's reflection should tell you that omnipotence and omniscience are mutually-exclusive traits, as well: you cannot possess both simultaneously; e.g. could God have the power to change the course of future events, or to change his mind?)
In addition to regretting making man, God failed in the objective of the Flood (eliminating the evil found in the hearts of mankind), so that raises questions of His omnipotence. He then expressed regret for destroying mankind, and thus rainbows were created (His promise never to do it again).
The story is completely out of character, as if DC Comics were to publish a Superman edition where he wore a Kryptonite ring "for strength"; talk about a continuity error!
All in all, you have a bunch of actions, words, and even thoughts (yes, the Genesis flood account says that God had certain emotions; were the authors of the account able to read the mind of God?) that are completely out of character for a supposedly "omniscient, omnipotent" God.
Such lack of perfection is the hallmark of human writers, who, in their rush to relay an ancient rainbow creation myth, screwed up the continuity for the supposed traits of God. The Old Testament is full of such discontinuities, which hardly reflects divine inspiration, but rather the words of humans writing with an agenda.