For a writer as prolific as she was - she wrote more than 50 books - that's not surprising. This unevenness was also, to some significant degree, the product of her political choices over nearly 70 years.
Lessing grew up in the profoundly racist society of Southern Rhodesia (now Zimbabwe) and her early reaction to that was to explore the complexities of inter-racial relationships in her first novel, The Grass is Singing, and then to join the tiny and secretive Communist Party (CP).
This difficult and strange work was published in London, shortly after her move there in the early 1950s, and it established her as a writer. It is very much a book of its time as it attempts to wrestle with the legacy of British colonialism and racism but remains caught in the ideas of its moment.
The Children of Violence series of novels, written between 1952 and 1969, chronicle this period in her life in thinly disguised autobiographical fashion, as both author and central character travel from Southern Africa through the conservative and repressive 1950s towards political involvement and on into the surge of anti-establishment activity that coalesced around CND at the end of the decade.
The first four novels grasp, for the first time, one of the central ideas of her work in this first phase - namely, the ways in which the different aspects of a life weave together into a complex fabric of political involvement, intellectual development and growing sexual awareness.
Another important idea for her future work starts to emerge in the final novel of the series, The Four-Gated City, as it moves from the present of the early 1960s to an imagined dystopian future which exists in the aftermath of a globally disastrous world war.
That upsurge of political awareness coincided with a major crisis in Western European Stalinism, when the Hungarian Revolution of 1956 was crushed by troops and tanks. Along with a significant number of other party members, Lessing resigned from the Communist Party and became associated with what was to become the New Left.
Breaking from the rigid orthodoxy of official CP thought, the New Left was marked by its eclecticism. Much of this was a positive development, as the ideas of Stalinism were subjected to a critique that drew on revolutionary Marxism. Much of this was negative, as Stalinism was equated with Marxism and both were rejected. For Lessing it represented both an opening up of her work and also the start of a rejection of Marxism.
The tension between these two aspects produced her finest work, The Golden Notebook. Here, the content and the form of the novel reveal how the apparently different aspects of a life are in fact woven into each other.
The four notebooks in which Anna, the central character, attempts to describe and separate the parts of her life are finally overcome by the notebook of the title, where all the elements are drawn together. This is the book's finest achievement. Its weakness is that it is, in the end, an almost quiet novel. When it should rage, it whispers.
The sequence of science fiction novels, published under the collective title Canopus in Argus between 1979 and 1983, shows how far her work had shifted from discussing socialist ideas and living in the real world to falling under the influence of Sufism and some of the dafter ideas that influenced the terrible film, Prometheus, in which human evolution is shaped and directed by extra-terrestrial forces.
Worse was to follow. The Good Terrorist represents a fundamental break in both Lessing's writing and her position within the cultural life of her adopted homeland.
It was the novel that sank her work into respectability. Published in 1985, it was nominated for the Booker Prize and marked the start of her move towards being awarded the Nobel Prize. It is also a terrible book.
It is badly written, especially when compared with her earlier work. It is snide and unpleasant about the British left. As Thatcher's assault on the miners and on the organised working class was hitting its peak, she chose to produce and publish this book.
It was a betrayal of us and of her previous self. No wonder a procession of reactionary literary journalists loved it.
I stopped reading her books after that. She made me laugh when I heard of her reaction to winning the Nobel Prize: she dropped her shopping in the street and said, "Oh, Christ!" And she did use the occasion of her Nobel lecture to raise money for an HIV charity that worked with children in Southern Africa. But who wouldn't make a gesture like that, given that opportunity?
It was a long slow sad decline for a writer whose early work has so much to admire. Read her early novels, for both their achievements as fiction and also as documents of a time when so much of our time was being forged. Don't bother with the later works.