“The Chi” was built around a series of shootings, and the way their repercussions rippled out through the lives of its large cast. But its best material was casual and observational. The testy relationships of the aspiring chef Brandon (Jason Mitchell) with his live-in girlfriend, Jerrika (Tiffany Boone), and his entrepreneurial frenemy Hannibal (Chris Lee) felt fresh. Even more original and entertaining were the story lines involving the middle schoolers Kevin (Alex Hibbert), Papa (Shamon Brown Jr.) and Maisha (Genesis Denise Hale), whose hilariously passive-aggressive pursuit of the mild-mannered Kevin was the show’s single best idea.

That first season can be streamed on Showtime’s website or through Amazon Prime Video. It’s necessary if you’re going to understand what’s going on in Season 2, and maybe it’s sufficient. Because through five episodes of the new season, a lot of the shine is gone from “The Chi.” The story lines are largely continuous: the fallout from the killing of Brandon’s younger brother by the tortured Ronnie (Ntare Guma Mbaho Mwine); the strife between the player Emmett (Jacob Latimore) and Tiffany (Hannaha Hall), the mother of his child; Brandon’s constantly stymied efforts to get his food-truck business off the ground.

But the urgency has faded from them, partly because of a sense that the bones of Season 1 are being gnawed over for too long, but mostly because the show’s sensitivity and unpredictability are, at almost every moment, shading over into conventional melodrama and self-conscious point making. As characters make speeches about fatherhood and police corruption, and we sit through stiff, sentimental flashbacks to Ronnie’s stressful return from military duty in the Middle East, the show starts to feel like an earlier Showtime drama set in Chicago, the buppie soap opera “Soul Food.”

The middle schoolers are still used for comic relief — selling candy bars to parishioners as they break a fast, engaging in a food fight on school picture day — but the situations have more of a tinny sitcom quality, and the young actors’ performances are correspondingly less joyful. (Hale still makes the most of every minute onscreen, though.) Mitchell and Latimore feel stuck, too, with Brandon’s and Emmett’s stories taking on a flattened, didactic tone they didn’t have in Season 1. The major new twist to the plot, a mystery element apparently involving gentrification, is playing out slowly but already feels forced into what’s been a distinctively organic narrative.

The cast turnover between seasons was small, though Sonja Sohn, as Brandon’s hard-edge mother, and Steven Williams, as an old-school gangbanger, are missed. The one big change was the replacement of the showrunner Elwood Reid by Ayanna Floyd Davis. Their producing and writing credits aren’t dissimilar — “The Bridge” and “Cold Case” for Reid, “Empire” and “Hannibal” for Davis — and it’s never a good idea to place too much credit or blame on one person in the ecosystem of a TV series. But chemistry matters, and in Season 2 the formula’s off.