The Cosby Show never got bad, but the earlier seasons are better than the latest ones.
Really, though, this is just my excuse to comment on how great the Cosby Show was. Even the lesser episodes are better than any sitcom on TV right now.
The Cosby Show is something I never really appreciated until I got much older.
At first, it was just a show I watched with my family at 8pm on Thursdays. I don't ever remember really being that excited to watch it, but it was enough to keep my attention, and I remember enjoying the more outlandish episodes (like when Cliff ate a sausage hoagi before bed or they tried to show Theo what the "real world" was like). Also I remember watching it in syndication as a kid, but that's more because there wasn't much on back in the late 80's/early 90's for a young kid, and it was something I was at least familiar with. As I got older, I probably ranked it in the same light as something like Family Matters or Full House or Perfect Strangers, an "adult" show (i.e. not a cartoon, or not a Saved by the Bell style kids show) that I liked enough when I was 10, but something I quickly outgrew. Definitely had no interest in watching re-runs any more when I was in junior high and high school.
But man, I didn't know what I was missing and how wrong I was about it. Started watching it in the early-to-mid 2000's as a grown adult, and now I'm thinking this show is hilarious. Sure I remember it being funny, but I don't remember it being
this funny, It has aged extremely well, and it has so many levels of humor. Like when Cliff makes a funny face or does something outlandish, ya that was funny for 10 year old me, but his delivery and the way he interacts with his wife and kids and others, that's hilarious for adult me.
I can't think of a show that aged better that both kids and adults could enjoy. Fresh Prince and the first several seasons of the Simpsons are the only other shows I can think of that I would say has aged well that audiences of all ages really could enjoy together, but they're not on the same level as the Cosby Show.
It's weird to say for a show that was the #1 ranked tv show for most of its run, but I think it's a very underrated and under-appreciated show today.