Book 2 of the Chronicles of Galen Sword. Unfortunately, the book ends all set up for Book 3, but the Reeves-Stevenses have NOT WRITTEN IT!!!! (and it's been ELEVEN years!)*
Ah well....maybe someday. While we are waiting, the first two are worth reading again, if you can find them. Like most SF/Fantasy novels, the back story is long and complicated and I won't even try to do it justice here. Suffice to say Galen Sword is lost in the wrong parallel world and is trying to get home. Vampires, shape-shifters and others of that ilk are in his way. Butts will be kicked.
*[ETA -- 11 years at the time I wrote this review, which was in 2002. I later discovered the third volume, Dark Hunter, was published sometime in 2003, but I have yet to read it.]