When you think of a great twist or a red herring or a way of misdirecting the reader, it is good, but you know that they are just tricks at the end of the day, and the way to keep interest is to write characters that people care about.
It's heretical, I know, but I've never really been able to get on with Agatha Christie. She is, of course, a giant of the genre, but I never feel that she cared a great deal about the characters. Consequently, neither do I.
When a crime writer thinks up a delicious twist, it is a great moment. Time to relax and take the rest of the day off. I do think that it can be overdone, however.