I would say that one immediate positive of Napoleon is that he is not afraid of seizing power. At a time when the other animals are gripped by a sense of what to do in a post- Jones farm setting, Napoleon understands clearly the implications of maximizing the moment and ensuring that he is able to put his stamp on it. While others such as Snowball are more concerned with the theoretical implications of ruling and power, Napoleon is much more practical in seeing the need to act in a decisive and intense manner. This can be seen as a positive. Certainly, the most negative element of his character is how he becomes chained to the idea of power. He simply falls in love with power and refuses to acquiesce any of it to anyone else. This helps to bring out a lust for power that results in the repression and killing of those who voice dissent. This has to be seen as a negative. Additionally, his desire for power is one where he no longer really even tries to discuss the elements of animalism. Rather, he becomes a new form of "Jones" in how he manages the farm and suppresses the animals. Here would be another negative element.
Although Napoleon is a tyrannical, violent, and oppressive leader throughout the novella Animal Farm, he does possess some positive character traits. Napoleon is a determined, ambitious, competitive pig. After Mr. Jones is expelled from the farm, Napoleon begins to plot how he is going to usurp power. Napoleon stops at nothing to become the supreme leader of Animal Farm and is willing to lie, kill, and intimidate the other animals in order to secure his position as leader. Napoleon is also intelligent and deflects attention towards Snowball whenever disaster strikes. He appoints Squealer to propagate lies and is able to gain the trust of some animals. Despite Napoleon's positive character traits, he is a selfish egomaniac. Napoleon physically and psychologically abuses the animals on the farm. He is not concerned with the well-being of the animals and they live in terrible conditions throughout his reign.