Spock's World features a plot that terrified the Trekkie in me: Will Vulcan cede from the Federation?
I'm not going to get too much into the plot (it would be too easy to create spoilers), but I will say that this novel plays with canon a little more than I'd like (AI computers? Really?). The dialogue between Kirk, Spock and Bones is cute (there are lots of "oh you silly humans/Vulcans" moments), but not particularly important.
Ultimately, I think the best part of this novel is not the issue of Vulcan cessation, but the incredibly thoughtful short stories about the evolution of Vulcan civilization: from the first Vulcan word to the birth of Spock. The beautifully crafted stories gave insight into a race that has struggled with its identity throughout it's history.
A must read for fans of Vulcan and ST: The Original Series.