They're very much a mixed bag, with part of the problem being that there's a lot of middling quality books that have major plot points to them. Good jumping on points would be:
Star Trek: Destiny - A crossover trilogy in which The Borg return to the Alpha Quadrant with the goal of extermination rather than assimilation. The events of these novels and their aftermath spread out across all the post-Nemesis novels and represent a major shift in the Trek storyline for years.
I've only been able to find the first of these, but it was quite good...I've also read several of the
Stargazer novels, the "Genesis Wave" TNG novels, along with the one where Geordi and Scotty team up again, and a few others...
I've also been enjoying the ST Enterprise novels from
Kobayashi Maru, through the Romulan War novels and now with the "Rise of the Federation" series...
Then there are the original crew novels from decades ago...such as the hardcover
Mission to Horatius, first of the novels to be released (back in 1968!), and the more recent series, which include some favorites such as
The Final Reflection,
Dreadnought! (less so, its sequel
Battlestations!),
Chain of Attack and its sequel,
The Final Nexus,
The Wounded Sky, the Rihannsu series,
Kobayashi Maru (where the stories of Scotty's, Sulu's, Chekov's and, of course, Kirk's turns at taking the stated test, what they did, and the results from that)...there were other good ones, but these are favorites that come immediately to mind...
Ruger