A bit sad, yes. However, this image does somewhat validate my decision to stop watching after season 13. When the DVDs were selling, I bought up to that season as well. This image is also missing seasons 32-35 which looks like there are some better rated episodes. I am sure there are funny bits in the later seasons, but I am not really interested anymore.
1 - Don't even waste your time
2 - Really really bad
3 - Has some good things, but mostly bad
4 - Fell flat quite a lot, but still enjoyable
5 - Mid/Average
6 - Decent
7 - Pretty good
8 - Good
9 - Great
10 - Masterpiece
So, from my list, it looks like it's been consistently okay, which is what I would expect from a show that has run as long as it has!
That's my personal rating system too. 5 I would literally not watch, 6 probably not either unless it is maybe close to 7 and something simple like some action flick. Haven't watched the Simpsons in a long long time though. I wasn't even aware it got this bad. Even before I quit people often said the "new" stuff wasn't that good but I still felt it was quite enjoyable most of the time. I guess at some point any successful product just becomes a milking process.
This comes real handy as I am watching The Simpson as a comedy relief series with my girlfriend for the first time ever (she watched several episodes, and I watched even less).