Content quality and the rate of submission has clearly plummeted. /r/all has become stagnant, and completely filled with memes and shitposts. Comment quality has amazingly gotten even worse (4chan level in a lot of cases), and there are definitely less participants on threads.
In comparison, I've found commentary in the fediverse to be more active, engaged, and positive than Reddit has ever been - and I was there since before Digg. My kbin feed, with a bit of tweaking and expansion out to other instances, is more useful by far than Reddit ever was, and it's activity level is beginning to match what used to be common on Reddit.
I think that Reddit was banking on not having a competing centralized corporate entity to absorb their users, and that it would prevent a Digg style exodus from their site. And to some extent, they were right - users, primarily readers still came back to reddit and have continued to do so because it's still the easiest place to find content on the internet. But, as you can see from the slow heat death of /r/all - that's changing.
What Spez didn't count on was that their moderators and content creators - the real engine behind Reddit - would leave. He assumed the thrill of having a large audience would be enough of a carrot to keep them participating while he made the site more difficult to use. This was a significant miscalculation, as anyone who's ever run a forum knows. Only about 2% of your users on a site will post, which means that if you alienate that 2% by any significant amount, you'll see a following degradation of non-participating readers as the content dries up.
Huffman should have realized this, as in Reddit's early days, he and the other admins on the site would regularly post with sockpuppet accounts to keep the content flowing enough to maintain readership. This mess is clearly of his own making, and one that he personally should have anticipated given what he and the other admins had to do to build the community in the first place.
But what's more interesting to me is what this (and the Twitter debacle) has done to illustrate the flaws of relying on centralized media. It's created a discussion about the wider internet and an interest in expanding it that hasn't been really talked about since the last decade. There was no reason to expand out from the centralized services as long as they were working well, fairly, and with an eye towards fostering their communities. It's when they moved into looking at their users as profit centers, and their moderation of content as a means of social control that it became clear that this contract of social responsibility had been broken.
And when that contract was broken, it broke the soul of Reddit's community. Nobody wants to contribute to Reddit, because Reddit isn't about creating a good space for the internet community to grow anymore. It's about how much money it can make Spez, and most of us really don't feel like working for him for free.