The answer is not much. Economic development is a progressive process, especially for large countries like China. Basically, you need to build the fundamentals before you can get into the faster development stage. Deng's reforms would not been possible if China doesn't already have an powerful industry and educated population to work with and it most certainly won't be able to protect its wealth if it doesn't have a powerful standing army and nuclear weapons. All these fundamentals are developed by Mao.
One of the common problem for other development nations today is that they try to skip Mao's stage of initial development and straight to Deng's opening up stage and got their economy and social stability destroyed because they don't have the strong fundamental structure to handle international competition.
Plus, as far as growth rate goes, Mao's era isn't bad at all.
Historical GDP of the People's Republic of China - Wikipedia, the free encyclopedia
Also, as far as China is concerned, the Great Leap forward is an lesson in proper management of country, especially on how to ensure there are proper monitoring mechanism in place so local situations and central awareness match each other. All the criticism is on the handling the situation, but not the overall direction of the event.
What is the overall direction of the Great Leap forward? To concentrate available capital and manpower of the nation and build basic necessities for a strong industrial base. In fact, it is because of the work during the Great Leap forward, such as drilling of Daqing oil field and first of China's chemical industrial plants, that China never suffered another famine afterwards.
Some people like to pass off great leap forward as a purely man-made disaster or something that is solely Mao's fault and completely ignore that there is a reason the disaster during Great Leap forward is actually called "three-years of nature disaster".
"4. 文献《干旱灾害对我国社会经济影响研究》研究中国农业旱灾的长时期(1950-2001年)变化,归纳认为:“受旱面积的7个高峰期为1958-1962 年、1972年、1978-1982年、1985-1989年、1991-1995年、1997年、1999-2001年,均在3000万亩以上。几个受 旱超过4000万亩的严重干旱年,如1959年、1960年、1961年、1978年、1986年、1988年、1989年、1991年、1992年、 1999年、2000年、2001年均出现在上述高峰期”。而1959-1961年的严重干旱,按时间序列居于诸高峰期的第一峰。
5.文献在对近500年典型场次特大旱灾及规律分析后,结论指出:“1874-1879,1959-1960年的大 旱,灾害等级为3级重旱,频率为100年一遇”;1990年代以来,“与1959-1963年相比,全国受灾面积尚未突破1959-1961三年特大持续 干旱时3812.5万公顷最低值。”
从资料和分析看,1959-1961年干旱灾害都是建国以来第一场连续多年的严重干旱灾害。
综上所述,1959-61,78,86,88-89年,灾区 人均减产粮食的绝对值和减产比例是十分严重的,将给人民生活和社会经济造成重大威胁。虽然,建国前期的灾区人均减产数额比70年代以来要小一些,但是当年 人均产量并不高,当地的减产幅度相当大,国家粮食储备力量相对薄弱,没有调剂周转粮食的更多余地。1959-1962年,是因旱灾减产幅度严重的第一高峰 期。以1952年以来的5年平均的人均口粮和减产常例计算,在1959-1961年连续三年每年多减产粮食达838万吨,减产幅度达15%,按以前口粮平 均消耗水平,大约空缺了2800万人口口粮。而这个减产幅度,是高于50年来同等受灾率条件下的减产幅度的。
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三年自然灾害_百度百科
I removed part of the text because it is out of format, the original article is in the link. Basically, while human error does play an effect, nature disaster is one of the main causes of the famine.