Same thing as JRHoch, I give it a few tries, then I'm gone. I might still follow the person if I like the art(there's this webtoons artist whose comic I can't bother to read but they draw so well I'm always looking at their twitter to see their promo art), but not the work itself, and that's kind of it. And life is too short to feel guilty that you don't like a work anymore, sometimes you just don't. If you have a HUGE issue and you think the creator is going off a cliff, maybe put it in very kind terms "Huh, X is being a very mean person to Y" (to describe OOC for example), but in the end it's their choices and mistakes to make.
Chances are they won't notice if they're big enough, it's just a lot of work and a lot of time that can't be spent chasing a lost fan. And if they're small and ask, sure thing I'll give my honest words and they do what they want with it (just like any criticism), but if they keep nagging me to try and change my mind then they might also lose my respect.