Piers Anthony's Xanth series. It hasn't ended yet, but I get the feeling that it just CAN'T end well.
I liked the series a lot, but somewhere around book 20-25, things took a turn for the absurd and annoying. Puns, puns, and more puns, to the point where whole pages are filled with pun people with pun names and pun talents. When reading any recent Xanth book, it's common to see the following passage at least a handful of times:
(protagonist) was walking along the enchanted path with no conflict or urgency, to the Good Magician's castle. S/He noticed someone walking the other way.
"Hi, I'm (protagonist) on my way to see Good Magician Humphrey."
"Hi, I'm (pun name), with the talent of (pun talent that fits pun name). I'm out here in the middle of nowhere for no reason whatsoever."
And then they just go on their merry *&^%ing way! And this will happen no less than 6 times, often more, sometimes stringing together 3 or more pun people in a row, just like that.
Mind you, this is forgetting all the pun plants and pun random creatures along the way. It was silly in book 15, it was cute in book 20, it's annoying in book 35.
And they way he gets these stories started has become - and I really do like the series, so this hurts to say - hackneyed. Lazy, even. The beginning of "Jumper Cable" quite literally starts with the main protagonist being brought into the story through a narrative hook. Our hero is just chillin' one day, when a big hook picks him up and drops him in the story. That's it. And then he decided to go to the Good Magician's castle, because that happens in about 95% of the books. Good Magician Humphrey is now little more than a plot device to get the narrative into full swing. One of the single most important characters in the Xanth universe, and all he does is tell the protagonist where to go.
Act 2 drags on with the characters interacting with each other with all the believability of mannequins in a soap opera. Puns and panty humor, maybe we see a recurring character or two, just to pad out the story for another couple paragraphs. Moving on.
Act 3, and the whole thing resolves without much urgency or tension. Day is saved, everyone falls in heterosexual happily-ever-after fairy *&^%ing tale love. The end. Bleh.
Maybe I'm just a crotchety young man of 24, but reading the recent books just huuurrrrts. I was right there with the series, all the way up through around book 25. Now, I just read them because, shoot, when you read 25 books in a series, you're more or less obligated to stick with it until the end.