This topic from Long and Short Reviews was a tough one, because when I start a series I usually finish it even if it is driving me mad. So I struggled to find one that I had actually given up on.
I did, however, find one.
"The Forest of Hands and Teeth".
I had never read a zombie novel before so I thought I would give the series a try. The first one I enjoyed, although I did notice a couple of points which should have given me an idea of where the series was going. Unfortunately these points became serious annoyances in the second novel, which is why I gave up.
The reason? The utter inertia of the characters. Nobody could make a decision, nobody could do anything, they just sat and agonised about everything. I spent most of the second novel screaming "Just DO something!" Needless to say, the third novel and the prequel remained unbought, because I couldn't face any more characters who let the world go past them.
So what led you to give up on a series?