I've heard much about David Brin's Uplift universe, most of it good. Sundiver is the ﬁrst novel in the Uplift series (which consists of two trilogies), and I was looking forward to reading it.
Unfortunately, it's bad. Ringworld-level bad - and for many of the same reasons.
The story serves as a passable introduction to the greater galactic politics in the Uplift universe. The galaxy is populated by myriad sapient beings, nearly all of which attained sapience by being Uplifted by a patron species. The ﬁrst known species to attain sapience was the near-mythical Progenitors, who then proceeded to Uplift a variety of higher animals they encountered. These, in turn, would then go on to Uplift other higher animals, bestowing intelligence, sapience and high technology across the galaxy. This process has been going on for two billion years, and a number of judicial and political practices are in place for governing the practice of Uplifting. When a species becomes Uplifted, it has to serve its patron species for a period of several hundred thousand years (or until the galactic community decides that it has exceeded the status of its patron).
There are very few non-Uplifted species around - and humanity appears to be one of them. This is rare - and in fact, tends to completely screw up the political and social order of Galactic society, because such a species does not ﬁt anywhere in the hierarchy established between patron and client species. One faction of humans believes that humans were Uplifted and then left behind by some long-lost mythical patron species - a view they share with some of the aliens in the Galactic society. In fact, humanity is itself in the process of Uplifting two client species - the dolphins and the chimpanzees - meaning that humanity is in the odd position of being a newly-discovered species that is itself considered a patron species.
The story itself is a combination of a scientific discovery story (extremely alien life has been discovered inside the Sun, aliens which some believe might be the patrons of humanity), a murder mystery and a political thriller. Unfortunately, trying to balance these threads turns it into a jumbled mess.
Brin's prose is utterly terrible. Stilted, overcomplicated, long words that serve no explanatory purpose. Gratuitous, arbitrary exclamation marks!!! Characters who talk (and think) as if they have a thesaurus cybernetically implanted into their language centres. Jarring, silly linguistic novelties that seem to make little sense and exist for no reason (for instance, men are consistently referred to as "mels" and women as "fems").
Most of the characters are ridiculous stereotypes, so the "reveals" in the mystery subplot are so expected that they just seem like stupid anticlimaxes. Who'd have guessed that the ill-tempered, manipulative, nasty, unpleasant alien with an ideological axe to grind turned out to be a villain?
The lead character is a Nivenesque übermensch (a trope that Brin himself is on record for despising). Most major events in the story seem like conceits to demonstrate just how awesome he is. He's brilliant, knows all there is to know about strange science, once saved (a major part of) the world, has Sherlock Holmes-level deductive abilities and is an expert unarmed ﬁghter too, why not?
The writing is incredibly sexist. Not quite as bad as Ringworld, but there is a wide spectrum between unproblematic and Ringworld, and unfortunately Sundiver falls on the ugly end of that scale. The ﬁrst female character with a major role gets introduced 70 pages in, and her ﬁrst action is to (literally) loudly proclaim her sexual availability. She's a badass military space pilot, who breaks down sobbing in her office and (literally) just wants a big strong man to hold her. And impregnate her too while he's at it, because it would be an honour for her to bear the awesome lead character's children. No, I'm not exaggerating or paraphrasing. In a historical retrospective we hear about a female triple Nobel laureate - and she's consistently referred to in terms of her sexual attractiveness. Much like Ringworld, it reads like its entire treatment of female characters was written with the consulting services of a focus group of particularly hormone-frenzied 15-year-olds.
The ending is abrupt and unsightly, and is probably best likened to a freight train hitting an especially nasty meat packing plant.
All in all, an incredibly bad story, told very poorly, set in a fascinating and interesting universe.