Macbeth is a tyrannical, frightened ruler whose fear of losing his ill-gained power leads him to destroy everyone around him who might resist him. He is so focused on the "scorpians" in his head (worries) that he couldn't have ruled adequately even if he wanted to. He had no vision for the country; he wanted the throne merely for the sake of having it; once he got it, he didn't know what to do except worry about keeping it.
He lacks virtue, and, though he does not have all the vices that Malcolm lists when he is pretending not to have the right nature to be king, he has some of the most serious vices for a king to have. He is a greedy, tyrannical and chaotic leader. Under his "care", Scotland is thrown into chaos.
As for how he treats people...he tells people that he will treat them well if they do as he asks; we don't see much evidence of that; however, we do see evidence of what happens if they don't (or if he even suspects that they won't). Banquo is killed after he says that he will help Macbeth, but only provided his honour and integrity remain intact. MacDuff is suspected a traitor after he does not attend Macbeth's coronation and, as a result, Macbeth orders Macduff's family destroyed.
He seems to genuinely care about his wife, but is too absorbed with his fear and doubt to maintain any semblance of a loving relationship. He has no close friends--the one person he seemed close to (Banquo)he ordered killed.
Everything abut Macbeth shows him to be a poor ruler.