When did The Simpsons stop being watchable?

After season 13, that was pretty much it, but there were noticeable cracks by season 11.

It hasn't.

Season 13-15 or so.

RIP
Lemmy
1945-2015

Season 1-10 great
Season 11-18 *beep*

Simprons movie + seasons 19-28 back to great.

1998

I still watch it every week, and they still do episodes that are pretty good, even if they aren't quite up to the standards of the early seasons. In fact, I think this week's episode was pretty decent. So I say never.

Back then in the early 2000's, it was logical to dismiss the new seasons because they didn't exactly use the kind of humor and heart-warming stuff that made us follow the show, but retrospectively, Season 11 is full of classics, not in the same league than the previous seasons, but entertaining, fun and overall, episodes that aged quite well.

I actually noticed a bigger drop in quality circa Season 15-16.

Darth Vader is scary and I  The Godfather

After Season 9, although there are some stinkers in 8 & 9 (and many all-time classics). The Citizen Kang Halloween special is the last good one, as well as being the best one.

Point them with the sticky end.