Hugo Chavez has become the so called champion of the poorest people of Venezuela, not because of any particular greatness on his part, but because he has very generously (and probably foolishly) lavished the oil wealth of his country on social programs and giveaways. While this has made roughly half the population fiercely loyal to him, and certainly right wing governments that preceded him perpetuated long term social injustices, Chavez' programs have done little to prepare the Venezuelan economy for anything like a diversified future. Their oil resources are limited, and expected to greatly diminish in the next three decades, so now is the time when great investments could be made in a sustainable economy. Instead, Chavez is merely investing in his own near term political future, and he has gutted many democratic institutions in the process as well.
This is in many ways a matter of opinion. Different people will have different views of Chavez's impact. From my point of view as an American, Chavez seems to have had a negative impact on Venezuela because of his attempts to take more and more power for himself.
Chavez sees himself as a "Bolivarian" who is going to make Venezuela free of outside influences, notably that of the US. He also believes that he is going to create a socialist state that will benefit the poor. To do these things, he seems to be trying to consolidate essentially all of the power in himself. For example, he has greatly reduced the power of lower levels of government, especially those in areas that do not support him. He has also cracked down hard on freedom of the press, trying to suppress media outlets that are critical of him.
By trying to reduce the level of democracy in Venezuela, Hugo Chavez has, in my mind, had a negative impact on the country.