In regard to characters, Marooned In Realtime seems to be in keeping with Vinge's style in the later A Fire Upon the Deep, but in such a short novel the superficial gloss he gives his characters actually works out quite well in this situation, since the main character has only been out "in realtime" for a matter of weeks after his "bobbling" so that he hardly knows any of the other low-techs, and the other advanced humans are so enigmatic and difficult to understand from his perspective.
The plot is interesting enough, although to warn real mystery readers, there is very little in the way of understandable clues to assist the reader with guessing who the murderer is. That part would be disappointing had the novel stretched to any length beyond its 269 pages, but again the light treatment of the novel allows this to work out well.
In regard to theme, the main point seems to be providing some sort of environment where the reader's can see with a semi-objective view how quickly technological advances are progressing - specifically, the rate of advancement is increasing at a pace never before seen on earth, and will likely continue unabated barring a planetary catastrophe. At this rate, given the amount of existing technology, it is even debatable whether a planetary catastrophe would do much beyond slowing the pace down for a few decades, provided that at least some of the human race survives.
Overall, the novel raises, but does not delve into, a number of different technological issues that are worth considering and debating, but its true value is as a light, smart read, with mostly likable characters and a pleasant ending.
