Koch's The Year of Living Dangerously was historically accurate without being a drag to read. It wasn't brilliant or even inspired writing, more workmanlike than that and with some rather annoying gimmicks. (I didn't like the constant references to 'the files' which didn't really add all that much to the novel and I believe could have been expressed better in other ways -- namely, conversation).
The characterization was solid but I never really got into the mind of the characters and was left grabbing at straws more often than to understand the particular motivations or actions of the characters. There also seemed to be a number of undeveloped plot threads, which seemed to be hinted at and then were never followed up, unfortunately. Also, Sukarno was beautifully crafted in the limited space he was given, you get a fairly reasonable impression of the man insofar as Bung Karno was a man.
That said, I liked the ability of the author to shape the characters around the events of Indonesian in 1965. The use of the wayang puppets was also rather effective at showing the subtle interplay between the different political factions without having to retreat into (what I imagine would have been) boring explanations which would have stopped or at least stilted the narrative flow.
That, and a few other things showed that the author had a deft understanding of the underlying subject material. It's a shame that the author didn't take the time to craft the wayang and other culturally appropriate elements more fully into the plot -- they could have easily been a plot within a plot themselves.
Whatever the case, it was a solid read and I quite enjoyed it. I don't think I would recommend it to just anybody. I believe that a grounding the subject material would make it significantly more desirable to read and an active interest in the period and the subject matter would make it indispensable to the reader. Otherwise, if you can borrow it from the library, perhaps consider it.
Could also be read concurrently with A Shadow Falls in the Heart of Java by Beatty which deals with similar issues in an accessible style (although it must be noted that it is a library borrow and not a purchase!).