I've just finished reading Relic and Reliquary back to back in the last few days (my son has been in the hospital with pancreatitis for over two weeks now, so I have a fair amount of time lately to just sit and read while I wait for things to happen). I liked Relic quite a bit, aside from one scene. There is a point towards the end of the book where the authors apparently decided that some exposition was required, and so they had three characters basically sit around and tell each other in great detail what they had all done five years earlier. It was clunky dialog that no human being would ever speak, and doubly so because none of the information was new to anyone involved in the conversation.
Reliquary, on the other hand, I thought was a real dud. In the same way that Star Trek writers continually fall back onto the "captain good, admiral bad" trope, it seemed like every single protagonist in the story had to deal with an immediate superior who was willfully ignorant. That happened in Relic to a much lesser extent, but in Reliquary I rapidly got tired of it. Also, the reveal at the climax as to the identity of the Big Bad was just ridiculous. It didn't come from any organic character progression, it was simply a random choice purely for the purpose of being a "twist" with no logic or substance behind it.
Honestly, if I didn't have my wife telling me how good the Pendergast books are I probably wouldn't bother to read another one.