I visited off and on from mid 2008 to maybe 2016. There were two very marked shifts in moderation during that time:
The first was in 2009-2010 when moot had to testify in federal court in regards to a kid who guessed Sarah Palin's yahoo email password and posted it on /b/. I am 100% positive that this resulted in a law enforcement/glownigger presence behind the scenes. The main reason I say this is primarily because CP spam disappeared overnight, but there was also an apparent change in what was and wasn't allowed to proliferate in terms of "board culture". There is no doubt in my mind that the Palin email thing put a lot of eyes on the site and moot acquiesced to cooperating with LEAs in order to keep himself out of legal trouble, and reigning in the site for that reason. This was around the time /pol/ was made as a containment board.
The second was in 2014-2015 when a tumblr user orchestrated a suicide hoax in response to raids from 4chan and gamergate in order to put heat on the site (basically, byuu). This had a similar effect, and there were rumors and leaks circulating in 2014-2015 that moot purged the existing staff and installed actual honest to god tumblr tranny jannies in response, this conspicuously coinciding with him dating some university sjw tumblrina and the creation of /lgbt/. This controversy and Gamergate in general obviously prompted his decision to clean the site up for sale, and thus a further enfaggoting of rule. This was also in the era of post-OWS idpol where media was driving attention to issues of race, sex, orientation, religion etc to distract from the wealth inequality and class disparity that had prompted OWS, and 4chan was once again a prime target. Moot folded and effectively Old Yellered the site and sold the corpse to a gook as dog meat, if you ask me 2015 was the year 4chan died for good.
And while I wasn't around for the pre-2008 era I can confirm that even in 2008 there was a felt sense of Eternal September 2.0 from the advent of the iphone putting normalfags on the internet -- /r9k/ was made to combat a perceived stagnation/repetition problem all the way back in 2008, as people were already bitching about low effort image macros like motivationals and advice dog etc.
So essentially you had the 2003-2007 era, the 2008 to 2010 era, the 2011 to 2015 era, and the 2016 onward era, each getting progressively shittier and more authoritarian and more calcified and homogenous in terms of memes and discussion and culture, and with the ratio of fun to slop steadily diminishing, such that regardless of what era you experienced, it was never as good as it used to be, but it always got worse afterward. That's why we all feel the same nostalgia for entirely different eras. Basically,
It's worth noting that these are just the conclusions I've come to through being there and a lot of subsequent conjecture, I'm very interested to see whether the /j/ leaks confirm or refute them.