The briefest possible review I can give of Helix is that it's essentially Ringworld done better. Like Ringworld, it's a Big Dumb Object story, featuring a very similar premise of a mysterious artificial world. In this case, we're dealing with a giant spiral structure consisting of thousands of interlinked cylindrical worldlets, all strung about a central star. Its influences from Ringworld are obvious and overt, and I won't be able to keep myself from making comparisons between the two stories throughout this review.
There are two concurrent plotlines, one concerned with the last humans alive, another with a community of aliens.
The human protagonists set out from a dying Earth, ravaged by environmental disaster and desperate wars over the last remaining resources, in a starship (the only such vessel ever constructed) with four thousand colonists plus a handful of technical crewmembers. After suffering a mid-voyage accident that damages their ship and kills a quarter of the cryogenically suspended colonists, they are forced to land on the eponymous Helix and try to ﬁnd a human-habitable worldlet on it.
A concurrent storyline concerns some of the inhabitants of the Helix, lemur-like aliens living under a strict theocratic society in the equivalent of the early Industrial Age. Our alien protagonist is the wealthy, brilliant heir to the business empire of airshipwrights founded by his father. He's also secretly an atheist, who despises the totalitarian rule of the Church and who tries his best to hide his lack of religious faith both from the Church officials he has to deal with in his business, and from his highly religious ﬁancée.
Unlike the ridiculous stereotypes in Ringworld, the human characters are actually believable characters with believable backgrounds, believable grievances, believable reactions to their situation, and believable interpersonal conflicts. Due to some past bad blood between some of the characters (and a case of mistaken identity), some of them outright hate each other. But - and this is really what I would expect from people who have been selected to take responsibility for the establishment of the ﬁrst (and likely only) extrasolar human colony - they're also professionals, capable of suspending their personal issues when the task demands it.
The human POV character is a middle-aged, overweight engineer with mildly depressive tendencies and who wouldn't be able to ﬁght to save his life. He's also a believably human being who grieves over the death of his loved ones and who struggles to come to terms with his situation. This makes him much more interesting than Niven's Captain Übermensch, Ph.D, because he doesn't always have the skills and abilities to handle the situation, so he has to work and think - and grow as a character - to get out of the scrapes he ends up in. He - again, in stark contrast to the Ringworld protagonist - frequently has to rely on the expertise of his crewmates to survive. This makes for much more interesting character interaction than in Ringworld.
One thing I did ﬁnd rather creepy was the romantic subplot between the POV character and one of his crewmates. Specifically, the fact that he kept referring to how she reminded him of his daughter.
Although Helix avoided much of what I hated about Ringworld, it did have its share of clichés, plot contrivances and implausible technical details. The ﬁrst that jumped out: How the hell does a starship survive atmospheric re-entry (and perform a successful landing) while going at near-lightspeed? How can a bunch of religious fanatics whose highest technological achievement is a Zeppelin analogue repair and operate a ultra-high-tech alien spaceship?
The Church - the main antagonists of the story - was essentially an organization of cartoon villains. They had no sympathetic qualities, no redeeming characteristics. Given that their thought policing was not effective enough to keep prominent members of society from turning atheist, how could people possibly have put up with their bullshit for so long? Their motivation seemed to be reducible to "they're evil because they're evil".
But the worst offense - the one that blew my suspension of disbelief and had me loudly exclaim "BULLSHIT!" - was the ability of one character to magically pick up alien languages and interface with alien technologies due to an ill-defined Magitech "smartware" brain implant. It seemed so wildly implausible that she might as well have had a Babel Fish - and it was very obviously a plot contrivance to allow the human and alien characters to talk.
Speaking of aliens, I also didn't much care for those. Put simply, they weren't alien. They were essentially just humans at various historical stages, except transplanted into lemur (and insect-lizard) bodies.
The Helix Builders were a complete disappointment and the ﬁnal meeting with them was entirely predictable.
I'd probably regard it as the literary equivalent of an entertaining B-movie. The science was implausible, there were too many clichés and obvious plot conveniences, the villains were cartoonish and the aliens were essentially guys in rubber suits. But there was also decent characterization, and unlike Ringworld, it wasn't mired in stupid sexist dreck.
I liked it, but it's hardly a great masterpiece.