I realize I'm late on this one, but one of my lasting memories of the 1980s is the Tripods television series, which then led me to read the books (although I think I never did get to When the Tripods Came)...I should fix that.
But this led me to explore Christopher's work further and as fun as the Tripods were, they were not his best work.
I give that title to 'The Death of Grass' (a novel that sometimes gets confused with the various post-apocalyptic novels of John Wyndham). Apocalyptic and post-apocalyptic novels involving plagues are common. In fact, the first post-apocalyptic novel (at least that was published and survived) was Mary Shelley's The Last Man, which created the trope of the one sole survivor of a global pandemic). The Death of Grass was different - the plague did not attack humans, but grasses. It was a dark, frighteningly pluasible novel and it was, in my opinion, what John Christopher should be remembered for.
His career was prolific. He wrote 70 novels under numerous pseudonyms, although only the John Christopher name is remembered (his real name was Samuel Youd). His death earlier this week robs us of another of science fiction's greats.