I read several Wyndham novels when I was 12 or 13 - this was one of them. My recollection of those novels was that they were enjoyable but tended to have poor endings, as if Wyndham had said what he wanted, got bored and just stopped. The exception was The Day of the Triffids which had a satisfactory ending. So how would I respond to re-reading Trouble with Lichen?
First I found it a good deal more sophisticated than memory had led me to believe: The book is a feminist tract, following the career of a strong, intelligent, visionary biochemist who uses the discovery of a lichen with anti-aging properties to start a revolution in the prospects for women not seen since the movement for universal suffrage.
Second I found it technically distinctive: The narrative is fast-paced and driven largely by dialogue and fabricated quotations from newspapers and BBC broadcasts. Characters (often un-named) are left to discuss the evolving events as representatives of an entire social class or profession or sex, reminding me of the general passages in The Grapes of Wrath (such as the salesman who can't get enough jalopies to shift on to migrating Oakies). Telephone conversations between characters replace descriptions of action. That said, Wyndham does describe some of the most dramatic action directly.
Thirdly, the ending, though abrupt, was fairly satisfactory, after all: Many SF writers would be more interested in describing the social consequences of a drug that can extend the expectation of life tremndously but that is not Wyndham is after - he wants to suggest that women are not merely ornaments or baby factories and the beginning of a social revolution gives him plenty of space to do so. He did indeed say what he wanted, then stop, but the resolution is fitting and pleasing.