God I've done this with so many shows that dropped quality abruptly.
- Heroes, halfway through season 3 I believe, that show just went off the rails so quickly
- Homeland, about halfway through season 3, similar to Heroes. Just so many eyerolling scenarios
- Shameless, 4 seasons, Emmy Rossums tits can only carry the show so far
- TWD, 6 seasons, I ended up hating every single character on the show
- Silicon Valley, 4 seasons, couldn't watch after Erlich Bachman left
- Arrow, 3 seasons, it turned comically bad
- Modern Family, 4 seasons, it got boring and repetitive after that and I stopped caring
- Dexter, 6 seasons, watched this 2 seasons too long. After the Trinity killer, the quality plummeted
- Arrested Development, 4 seasons, I should have never watched the Netflix version, it was such a downgrade
- ER, 4 seasons, it goes from a fairly realistic over-dramatized medical drama to completely off the rails, but those first few seasons are still some of the best television I've seen. "Love's Labour Lost" is the best and also most terrifying episode of any show I have ever seen.
- The West Wing, 4 and a half seasons, just wasn't the same after Rob Lowe and Aaron Sorkin left. Like ER, some of the best episodes ever on TV were in those first 4 seasons.