Honestly, I don't understand the people who are bitter about the way Agatha All Along ended. I thought it was freaking amazing.
Agatha and Rio got to be angry and in love and epically drawn to each other. And petty as all hell.
We got a kiss (and Rio's face those seconds before Agatha kissed her and she felt it coming). We got to see the wounds Agatha left in Death. We got to see a moment where Agatha essentially forgave Death (even if she wouldn't acknowledge it to Rio). We watched Rio cover her grave in the color that meant most to Agatha. We watched how Rio gave Agatha the time to love her son (because even if the older Agatha refused to see it - because it hurt too much - she would clearly have taken that gift a second time if she found herself back in that moment).
And it wasn't even the end of them, because if you don't think Rio is going to keep pursuing Agatha's soul now that she's floating around as a ghost instead of coming home to her, you're wrong (you're just... wrong).
It might not have been a "happy ending" but it was freaking glorious.