The best Trek novel thus far, bar none. There's a number that are in the running for the number two position but none are capable of catching The Final Reflection.
The Klingons come alive in a way that the TV series never managed to. Their culture is diverse and very different from what is usually portrayed in Trek and yet still true to the TOS version of the Klingons. Much more believable than the biker Klingons where almost everyone seems to be a warriors portrayal that we got.
If you want more background, see if you can find a copy of the FASA rpg Klingons supplement. It was written in parallel with TFR and gives even more insight into the best portrayal of an alien race ever in Trek lit.