To get the obligatory cavil out of the way: A World of Difference is of course best known, at least to sf historians, as a 1955 novel by Robert Conquest. Another established title that's gone the way of Sir Arthur Conan Doyle's The Lost World, John Buchan's Greenmantle, Charles Williams's War in Heaven and others ...
I always expect Harry Turtledove to whelm me with frighteningly erudite alternate history, leading to worrying suspicions that the mere presence of practically any named character may in fact be a bit of brilliantly incisive historical irony which I would notice if only I'd learned the appropriate period. Soothingly, however, this venture is into a more Stephen Baxterish realm of alternate astronomy. Just as Garry Kilworth's "Navigator Kings" fantasies moved Britain to the position of New Zealand for the sake of some Celtic-Polynesian action, so Turtledove has quietly replaced Mars with the larger, more interesting and definitely habitable planet Minerva.
History presumably starts to diverge significantly when the Viking I lander touches down on Minerva in 1976, and transmits back to Earth an epoch-making picture of the terrified Minervan native who is busily beating it to death with a stick (identified by our resourceful scientists as "the Artifact"). Because of this or some earlier effect of Minerva's existence, the ripples along the timestream – like the beating of that damned butterfly's wings – cut short one notable career: "Too bad Gorbachev had only lasted nine months. Tolmasov still wondered if his cerebral hemorrhage had been of the 5.54mm variety."
Thus, with what looks like a certain nostalgia for the old Cold War enemy, Turtledove magically restores the Soviet Union and the traditional US/USSR friction in his presumed 1990s – as a joint Minervan expedition heads across space in separate manned craft, Athena and Tsiolkovsky. Some NASA double-dealing leads to a late course correction for Athena, which lands as close as possible to the Viking touchdown site and its Minervan community ... while the Soviets find themselves in an adjacent country on the far side of an impassable-seeming canyon, making contact with a different Minervan group. Since the "Soviet" Minervans have already declared the equivalent of war on the "American" ones, the stage is set for an interesting game of military advisers.
The Minervans themselves are engaging creations, conscientiously imagined in a physical sense. Radially symmetrical, they have six legs, six arms and six eyestalks, allowing a six-level graded approach to averting one's gaze or to idioms like "I've got my eye on you." Turning all one's eyestalks away from someone is extremely pointed, and there's a carefully calculated measure of interest in "Let me turn three eyes on him." Minervans may not have heard of ostriches, but are handy with proverbs like "pulling in my eyestalks won't make it go away." In other words, beneath the scanty disguise of a few routine quirks like this, the Minervans are likeable in a very human rather than an alien way. There is no hint, for example, of six-valued logic or radial patterns of thought – as disconcertingly imagined by Naomi Mitchison when describing starfish aliens in Memoirs of a Spacewoman (1962).
Both contact teams' interactions with the natives are interesting enough. The Americans incline to humane concerns, and, in a subplot straight out of James White's "Sector General" space-hospital sequence, one of them plans crude stratagems against the racial tragedy of all Minervan fauna, whose females invariably die in childbirth. Meanwhile the Soviets, though infested with KGB agents and some awful dialogue ("Would it not accord well with Marxist-Leninist principles to render fraternal assistance to this advanced society in its struggle against the oppressive feudal aristocrats on the eastern side of Jötun Canyon?" I am not making this up), are decent folk at heart. Unfortunately they make the mistake of letting their aggressive Minervan comrades see a Kalashnikov in action....
So we come to the inevitable culminating battle, cunningly timed for just when the most likeable female Minervan (and precociously the world's first feminist) is due to give birth. Can the aggressors' superior numbers and powerful secret weapons, both home-grown and annexed from their visitors, possibly win out against the nice Minervan defenders' skimpy resources of US handguns, a microlite plane, and good old American know-how? Is the Pope a Scientologist? But it's an entertaining read, and caused me no pain.
A follow-up letter to the magazine:
Here's a footnote to my review of Harry Turtledove's A World of Difference (NYRSF #123), which suggested a gulf between this rather simplistic novel and the alternate-historical erudition for which the author is better known. Some British readers had even speculated that it was an old MS dusted off and sold in the wake of Turtledove's successes. In fact, as noted in the SF Encyclopedia, the US first edition was in 1989; the British publishers confused the issue (or at any rate the reviewer) with a mendacious 1998 copyright notice.