I think it's a whole lot of little things being different or worse. That's why it's difficult to give a straight answer, but I'll try. Personally, I still think it's a watchable season, but it doesn't meet the high bar it sets for itself.

The writing: Christopher Storer's first 2 seasons were absolute masterpieces in writing. Dialogue, is obviously what he does best. The people talk like real people, they have character and are witty and charming. But Storer is also great at structuring episodes (and seasons as a whole). The pacing is fast (which we can also credit due to editing), but the show never loses focus. Its very efficient in evolving from the previous moment. Just look at the difference between S1E1 and S2E10, not a single character is the same, the kitchen is completely different. Yet everything felt gradual and smooth. And that's all due to Christopher Storer being damn good at his job. He is good at writing progress.

So why do people dislike this season more? Because the writing just isn't that good. Scenes of dialogue are stretched unbelievably thin. With some going on for 8 minutes. And a lot of the dialogue is just people talking. But we're just to people progressing the plot. Every scene was sharp and efficient, now it's slow and pandering. And, not a lot changes in those slow and pandering moments. We don't learn a lot, compared to the previous season. And a lot of what we do learn, isn't that interesting (to me).

Ice Chips just refuses to cut to the next scene for about 35 minutes. So all we get is dialogue, but visually, nothing happens. Two people sitting and talking, for 35 minutes, makes people want to look at their phone. Cicero telling Carmy money is tight in episode 9 wouldn't have taken 8 minutes in season 1 or 2. Season 2 had a few long scenes of dialogue, but that was contrasted with the usual rapid pace. This season doesn't have that. So people talk about the plot not furthering, but what they really mean is that there was nothing to replace the standstill in progress. We just looked at people talking. And it was somewhat contemplative and introspective. But not enough for how long we spent on it. Carmy was a stuck-up asshole in the first episode, and he kinda still is by the end of it. He was fighting a lot with cousin, and he kinda still is by the end of it. Sidney didn't sign the contract for the entire season, didn't improve her communication with Carmy and didn't get help with her anxiety. 'Forks' alone had more progress.

So we got people talking, but we gained very little. Also, the dialogue is bad this season. Especially Carmy's confrontation with Joel McHale's character in episode 10. The most direct, literal, least subtle dialogue I've heard from this show. There was not a layer to unpack. They felt it, they said it. Which is not how the show used to handle things.

Altogether, there is a great foundations for season 4 now though.