I wrote series rather than television show on purpose, as I am perfectly okay with talking about books or even movies in this thread.
I’ll start with Law & Order: Special Victims Unit. I can’t say I ever loved it the way I loved its often brilliant progenitor, but it was reliably good television for a good part of its run. Not now, though. (Or at least not as of two years ago, when I started immediately turning off the TV if it was on.) Nowadays they seem to be addicted to pointless twists, gratuituous gore, and rape porn. It turns my stomach.
Some time ago my daughter decided SVU was not a crime suspense/detective show, but rather a psychological study examining how many times Benson, Stabler and the rest of them could endure having cases blow up in their faces, with everything they tried just making things worse. Given that Stabler ended up quitting the force after shooting a teeneager, her interpretation may be right.
It used to be about Medical Mystery of the Week, and now it’s about detox and who’s sleeping with who. Not that I don’t tune in now and then to get a dose of House snark.
Yeah, it was cheesy but I enjoyed it for a couple of seasons, liked some of the characters. Then the female lead got some sort of face changing plastic surgery over the summer break and I could never watch it again.
I couldn’t follow along. It wasn’t that it was a botch job. But every time her face was on the screen, instead of hearing her lines, my mind was busy searching for what, exactly it was that made her face look, different or unnatural or weird. In the end I just stopped watching. At some point in the show I would realize I didn’t know what was going on any more, it was that distracting.
The Thomas Covenant books by Donaldson. I read them twenty year ago and liked them. Now, when Donaldson came out with new books in the series, I just felt a little ill about them. There’s no way I want to continue immersing myself in that world. Just no.
I grew up with this series and thought it was the funniest thing in the world. I watched reruns about 7 or so years ago and thought it was the unfunniest “insert stupid oneliner here” writing that didn’t even have funny situations.
House, for many of the same reasons that teela brown posted. When House ended up with Cuddy at the end of (IIRC) Season Five, I started drifting away from the series. Not because I thought it was a bad thing, but because I thought it was a natural stopping point, and anything beyond it would probably be less than compelling. And. . .it was, so I stopped watching altogether.
I really liked Kage Baker’s Company series through the fifth book. I sort of forced myself through all the ones after it.
*Sopranos *after season 3 or 4 or whenever the dreams started.
*True Blood *is one decision away from being that for me. I won’t spoil anything for anyone catching up, but if a certain person isn’t dead, then they can all walk into the sunlight bound in silver and roast. I may still quit watching anyway, but they have me for the first ep of the next season. How I Met Your Mother put it to bed with Lilly, she freaking exhausted all the time. As are all the jokes… I will try to take Robin to bed though, yowsa! she is still smoking.
Grey’s Anatomy It was never a good show, but it was somewhat watchable for a couple of seasons, then both my wife and I both just stopped as each character became so unlikable and unbelievable.
Heroes is an example of a show that made itself unwatchable.
The first season was outstanding, but when they stopped singing the words to the theme song in the 2nd season, I just couldn’t enjoy it anymore. Even making the 2nd season color instead of black and white didn’t compensate.
Though Wrangler Jane was hotter in the 2nd season.
It’s my own fault because I didn’t specify in the OP, but I really had in mind instances in which the series changed rather than your tastes changing.
For example: I still think the first several seasons of L&O:SVU are worth watching; but as the show evolved, it grew more and more ridiculous. I pretty much gave up on it when they sent Benson to prison undercover so she could find a rapist corrections officer, because it was so blatantly exploitative. But even before then the continual pointless twists and unending grimness made the show more and more like eating grease.
ETA: But, again, I should have been clearer in the OP. People who responded as Sir T-Cups did are neither hijacking nor threadshitting, as his interpretation is quite reasonable.
I really loved Malcolm in the Middle in the first one or two seasons. It quickly got annoying and then became unwatchable. I now find it completely unbearable.
NCIS. I really enjoyed it for a long time, but it is just so formulaic and repetitive, and the characters are (mostly) not allowed to grow or change. Abby, especially, makes me cringe.
2-1/2 Men - I am embarrased to say that I used to enjoy watching this show, because it made me laugh. It was formulaic and sit-com-y, but I like the premise, I liked some of the characters (basically everyone except the two men). After what’s-his-name went off the deep end, though, I lost my taste for it, even for the re-runs.
How I Met Your Mother - it was funny for a couple of years, but I just got tired of the manufactured problems and life-issues of five unrealistically attractive and clueless people. I still want a bright yellow umbrella for myself, though.
So many shows like this. I just can’t watch much TV any more, most of it is truly a waste of time.
Roddy