Reading Helliconia Spring when it first came out in 1982, when I was 15, was tremendously exciting. I last reread it, along with the other two, on holiday in Croatia in 1996, I think. I'm glad to say that it pretty much stands the test of time. It is in two parts, the first being the short tale of Yuli, who escapes the (vividly drawn) theocratic underground city of Pannoval (I was sorry that we saw no more of it) to bring new expertise to the town which becomes known as Oldorando, and the second, many generations later, being the story of how the people of Oldorando adapt to the coming of Spring. We readers are told what is going on in terms of climate change, but the characters are in the situation of their world gradually (and sometimes suddenly) changing out of all recognition.
Helliconia Spring popped up on my reading list again thanks to having won the BSFA Award in 1983 (beating a pretty tough field: Little, Big, Nebula-winning No Enemy But Time, Philip K. Dick's The Divine Invasion and Gene Wolfe's The Sword of the Lictor; the Hugo that year went to Foundation's Edge). It also won the Campbell Memorial Award (again beating No Enemy But Time).
Helliconia Summer also still worked for me - the twist here is that the Earth observation satellite sends a volunteer from its crew to the surface of Helliconia, where he knows he will not survive long due to a lack of immunity from local diseases, but gets very much mixed up in a complex dynastic / political / gendered dispute among local rulers. Aldiss plays the theme of technologically advanced individual failing to impress a much more medieval civilisation very nicely. It didn't win any awards, the BSFA going that year to Tik-Tok.
On the other hand, Helliconia Winter didn't work for me anything like as well as the first two. I found the plot meandering, the gender politics pretty unpleasant, and the Earth observation sections taken in unwelcome and not very interesting directions. I may be in a minority; it also won the BSFA award, though I must say I have not heard of three of its four opponents - Free Live Free by Gene Wolfe, Kiteworld by Keith Roberts and The Warrior Who Carried Life, by Geoff Ryman, though of course I know other work by all three authors. The other BSFA nominee that year was The Anubis Gates, by Tim Powers, which I read and loved when it came out. The Hugo and Nebula that year both went to Neuromancer. None of the BSFA shortlist was on either the Hugo or Nebula ballots.
Anyway, a refreshing return to an old favourite.