Many of the other posters have already given a synopsis of what the plot is for this book, so I'll jump into my review:
THE GOOD:
-Uhura is in command, and we get to hear her dish out commands after the previous "commander," Sulu, goes out of commission due to a time/space issue that hits the ship.
-Sulu is in command.
Even though we know he will eventually get his own ship in the onscreen canon, it's still interesting to see him handle things while Kirk, Spock, and Scotty are off the ship.
-The aliens of Farezzi. They had a unique way of speaking, as well as a unique look.
-Many of the minor Enterprise characters from The Original Series show up.
THE BAD:
-Too many of the characters from The Original Series episodes turn up, as well as new characters. Unfortunately, since there are so many characters, no one is given their unique voice, or a clear picture of how they look.
Sometimes, it wasn't clear what gender the new characters were, until later in the novel when they may be referred to as "him" or "her." For casual Star Trek fans, even the minor characters seen onscreen may be unfamiliar, and add to the confusion of trying keeping up with everyone.
-While trying to keep track with the many characters, it's not always easy to actually figure out what is going on, or where they characters are at certain points. For instance, near the end of the book, it was understood that they set up a "bridge" in sickbay due to the problems on the primary bridge as well as the auxilery control room. And, given that there were so many casualties, and sickbay had a lot of people going back and forth, it wasn't clear how the improptu bridge was able to run.
There were others: For instance a dogfight between two shuttles and alien fighters, where it wasn't clear whether they were still on the planet they initially came to or in space.
THE UGLY:
-Too many characters + too much going on = overloaded book