Embrace the darkness, it comes with sopaipillas
If The Fractured But Whole was comparable to "some of the show's best multi-episode arcs," then From Dusk Till Casa Bonita is like a great standalone episode.
It's a fantastic parody premise, adapting the idea of From Dusk Till Dawn to South Park's vamp kids and the - believe it or not, non-fictional - Casa Bonita restaurant. This sets up some pitch-perfect "South Park moments" juxtaposing the dark and supernatural with a food court and a mariachi band.
Especially the final boss,
As for gameplay, this DLC benefits from keeping itself constrained: it restricts you to one new class (with in-theme abilities), locks down your party (including newcomer Henrietta), and uses but doesn't change your fart-time powers. It strikes a great balance between new and old ideas and streamlines the game's pre-existing sprawl of class and party options.
Its "world," that is, the Casa Bonita restaurant - including an arcade and Black Bart's Cave! - does lack the main game's open-world scale and its abundance of South Park references. But it does still manage to fit a little non-linearity into this small space, allowing you to collect some vampire relics in whatever order you like.
From Dusk Till Casa Bonita is a short, but functionally-complete slice of gamified South Park. I'd love to see more self-contained stories like this one.
Better than: Mass Effect 3: Leviathan, South Park: The Stick of Truth (yeah, the full game!)
Not as good as: Mass Effect 3: Citadel, South Park: The Fractured But Whole
Spoiler alert: There's only one more self-contained story like this one.