I only had a passing interest in the show when I was younger, and I enjoyed playing some of the video games simply because I knew they were associated with the show. But I think I was too young to really "get" the Simpsons back then, so it didn't hold my interest like other cartoons.
About 2 or 3 years ago, I decided to sit down and really give the show a fair chance. I started collecting and binge watching the series with the DVD box sets. I really found myself hooked on the show, and eventually bought the first 10 or so seasons, watching them all in order. I would agree with most, in saying that the 90s really seemed to be the golden era of the show. Many of the seasons were very solid back to back. However, I noticed that around season 10 or so, the writing started to change a bit. I believe the show suffered from a lot of the same mistakes as other long-running shows. The creators want to take things in a different direction eventually, and it's a very delicate balance.
What always bothers me is when they start writing the characters in a way that totally conflicts with what you've come to "believe" about the universe they've created, the characters, the dialog. Once they start to tinker with that, it's a turn-off. I felt like what I was perceiving was more like the writers reaction to then up and coming shows, like Family Guy. By season 10, everything started to get way over-the-top for all of the standards that were established in the first 9 seasons. It kind of felt like they weren't taking the show as seriously as they had been. A lot of that subtle, witty humor was replaced with a lot of fast-paced absurdity and out of context gags, which is why I say that the show felt more like a Family Guy type deal. I remember being disappointed to find out in one episode that Skinner wasn't actually the person he said he was, or at least, was no longer the character they original wrote him as.
I've heard a lot of the later seasons were brought down by so many episodes based around a lot high profile celebrities. Rather than poking fun at American pop culture and celebrities, they were later embracing and incorporating a lot of that stuff into the show. I've not gotten that far at all into the 2000s era as of yet, but with the changes I've seen, and the things I've heard about the show's downturn, I'm not exactly that excited to continue watching. Although I am happy they've decided to continue releasing the box sets again, after a production hiatus they had taken for several years.