I know a lot of people used to talk about the 30 page rule or the 3 chapter rule - how much of a book you have to read before you decide its DNF. My new rule is = if I don't like the MC by chapter 2, I'm not going to like her or him. I love mystery, suspense, thriller but lately those have also been my top DNFs and mostly because (other than the annoying present tense form) I just don't like the MC. Usually a woman. Usually try to explain that she's been through stuff which maybe warped her character, but all I know is that I don't spend my precious time with flesh and blood people I don't like, why would I spend my precious time with paper and ink people I don't like? Just my ranting.
I'm with you, Barbara. I recently started reading the new Michael Connelly novel, Nightshade. I read a couple of chapters and didn't recognize any of his usual characters. I discovered that this novel has a new main character and I thought, OK, I'll give him a try. Two-thirds of the way through (I like Connelly, so I gave him a good try) I realized I was bored and didn't care what happened to the main character or any secondary character, so I stopped reading. Life's too short to waste my time.
Oh, gosh. I just loaded a story into my kindle - and as an aside, why is every psychological suspense novel billed as "an unputdownable page turner with a jaw dropping twist"? - and I'm a couple chapters in, the MC is going off to The Remote Location - with a guy she barely knows, whom she dumped her former bf for because this new guy was so handsome wonderful, etc, but then she's describing his behavior on this trip (did I mention that it was to a Remote Location?) and he's short tempered, controlling,inconsiderate and rude. I think in the current crop of psycho suspense, this is what passes for "a keeper."
I will sometimes skim to see if anything promising crops up and then go back and give in one more try, but there are just too many books, too little time. My DNF rule is the LTS - Life's Too Short - rule.
Just my ranting.