British sf grandmaster Aldiss offers a big, ambitious, colorful, but only partly successful multi-generational saga--the first of a trilogy. Planet Helliconia orbits one sun of a double star system, so the seasons last for centuries; as the story opens, glaciated Helliconia is emerging from its long intense winter. The vigorous, complex Helliconian ecology is vividly drawn--with conflicts among humans, variant humans, and the alien phagors (horned, bipedal, shaggy, noxious, hereditary enemies of humankind) that recall the organisms in Aldiss' early masterpiece Hothouse. And, as the climate rapidly warms, Helliconian life undergoing an explosive transformation from cold to heat adaptation, the human settlement of Oldorando encompasses the usual human-interest dramas: leadership crises; murderous disputes; female emancipation (the women attempt to gather and extend knowledge, much to the disgust of the men); sexual rivalry; plague; and an invasion of phagors --as the settlement itself grows from a squalid hamlet into a seething medieval-style city. (Also, in an archly didactic touch, Aldiss has scientists aboard a satellite studying the transformation below while televising the proceedings back to Earth, where the transmission arrives a milennium later.) So: no shortage of fascinating material--but the panoramic cast of characters discourages any intense focus, the often-lumpy prose doesn't help, and the whole impressive enterprise never quite catches fire.