I found Field Gray to be a page turner. I just love the character of Bernie and can't get enough of him. I don't understand Bernie's relationship with Erich Mielke. I too am trying to make sense of the ending. I will read the next book right away.
Field Gray is my favorite of the series. In fact, I've read it twice. The first time was right after finishing the trilogy, Berlin Noir, and needed to read more Bernie immediately regardless of where it fell in the series. After that I read books 4, 5 & 6 in order followed by Field Gray again (in order this time). I liked it just as much the second time and was able to make better sense of some of the twists. The section that details Bernie's time in the Soviet POW camp is memorable, as is the gunfight on the train against Mielke's would-be assassin. Not just a great book in the series, but a great book period.