After more than 15 years of standalone episodes, South Park embraced episode-to-episode continuity in Season 18, most memorably with a multi-episode arc about Randy Marsh as Lorde (ya ya ya). Each season since then has had varying degrees of serialization. At the tight end of the spectrum was Season 20, which told a season-long story about the 2016 election, following Mr. Garrison's racism-fueled presidential run aided by internet trolls and the seductive power of nostalgia for a less complicated world ("member when there weren't so many Mexicans?"). At the looser end, the just-concluded 22nd season carried a handful of plot lines across the episodes with only a few mostly standalone episodes mixed in (I say "mostly standalone" because even these episodes factored into the larger storylines).
The best iterations of serialization were Season 19, which introduced PC Principal and skewered PC culture in a way that felt cathartic in 2015, and the aforementioned Season 20. But Season 22 was less successful, with the light serialization making it feel overstuffed and under-focused. It sometimes had the feeling of "this isn't quite working, so let's add something else in and see if that helps." South Park always has so many ideas that carrying them across episodes makes the show feel chaotic, like there's just too much going on. It's enough to make one yearn for the simpler times when maybe there was one three-part episode every now and then. (member Imaginationland?)
Season 22 was 40 percent serialized and 60 percent standalone, and both types of storytelling were uneven. The five mostly standalone episodes that started the season were all moment-to-moment, with smart scenes like Randy and Stan's disinterest in yet another shooting at South Park Elementary sharing episode space with tired, drawn-out bits like Stan's attempts to signal to people that Sharon was upset about the mass shootings because she was on her period. I've already completely forgotten what "The Scoots" was about, but the dark and dirty jokes in "A Boy and a Priest" were vintage South Park.
Sometimes the threads that carried throughout the season were the focus of entire episodes and they often receded into the periphery, and not all of them were fruitful. Cartman's quest to prove that Token had seen and didn't like Black Panther wasn't that funny, nor was the town's fixation on Red Dead Redemption 2. (I admit that my personal lack of interest in superheroes and video games colors my opinion here). It was pretty striking to see Trey Parker and Matt Stone (sort of) apologize to Al Gore for not taking his warning about climate change more seriously in 2006 with the return of ManBearPig, but that storyline devolved into nonsense and violence that was gratuitous even by South Park standards. The Amazon storyline that ran through the last two episodes contained the season's sharpest bit of social commentary — using the old coal miner's anthem "Sixteen Tons" to soundtrack the exploitative modern-day toil of working in an Amazon fulfillment center — and accurately skewered a corporation that needed skewering, but it also wasted a lot of time on the kids' bike parade, which was intentionally unimportant.
Two things are true about South Park in 2018. One is that your enjoyment is largely dependent on whether or not you agree with the sociopolitical point Parker and Stone are making. The other is that Parker and Stone have earned the right to do whatever they want. If they want to do fully serialized, they can; if they want to go back to all standalone, that's up to them; if they want to keep doing exactly what they've been doing, no one can stop them. But as someone who's going to watch whatever they do because that's what I've done since I was a kid, I would like for them to lock in on something. They're still capable of brilliance when they do.
South Park will return for Season 23 in 2019.