I actually enjoyed the yahoo season a lot.
I've gone through Community now, and I can say that the first three seasons are gold.
The third found a way to self reference their rehashing and product placement as a means to an end, and was superb in terms of witty, irony-laden writing.
Then I started watching the fourth season, and you could tell that everyone was off. They were saying and doing things that weren't really funny or smart, more like being told what to do by a bad impressionist doing Dan Harmon stuff. Which is weird, because they still had a lot of the same writers and directors, and actors obviously. When the characters started saying stuff like "i hate self reference humor", they weren't really taking the subject and pulling it apart anymore, they were just telling you what you already knew.
The fifth season was good, but Troy leaving kind of killed the show for me. The dynamic was totally off, and Abed became a depressing background character doing goofy shit instead of the grounded metabot who instructed the audience on everything awesome while kickin' it with his best bud.
The sixth season is okay, but you can tell that Dan was now busy doing Rick and Morty shit and the show suffered from it. The 28 minute Honda commercial was no where as good as the Subway stuff. It ended up getting creepy.
Honestly? They seemed to have made so many "would be" finales because of the ratings and their perpetual wonder if they'd make it the next year. At this point, I kind of like to think the series ended after the Season 3 finale, and the rest is kind of like DLC. It works well.