I gave StF an average rating, also. I'd been a little behind in my Titan reading, so I read the last three in a row to be ready for the Titan installment of the Typhon Pact series. Seize the Fire just didn't measure up very well by comparison.
As others have mentioned, I felt that many of the characterizations were off, especially Vale (goofy and inappropriate comments falling out of her mouth) and Riker (OK, fooling the hostage-taking Gorn did seem somewhat Riker-like, but going to the Gorn ship just made no sense whatsoever).
Beyond the characterizations, there were other implausibilities and inconsistencies that really made it difficult to just go along for the ride. When Riker decided to send the landing party to the planet surface, I actually involuntarily exclaimed, "Oh, brother!" out loud, making my wife ask what was wrong. It just made no sense, given the rest of the situation at that point. Then, Ssyrex's belief that the ecosculptor was the Gorn deity came out of nowhere, and was completely unnecessary. And then, later in the book, the Gorn captain mentions the possibility, when there was NEVER any indication that Ssyrex had mentioned it to anyone on the Gorn ship. Inconsistent and irritating.
Thinking about it again, maybe my "average" rating was too high...