One thing I will say and this, of course, is pure opinion on my part. Outside of writing, production, and acting - all major components that contribute to the success/failure of these shows, the attitude of the actors is key. Every actor on set appeared to enjoy making these episodes. I’ve watched some shows and movies where it looked like everyone was just going through the motions and couldn’t care less, and it negatively impacted the quality of the product.
Not Agatha All Along - they looked like they had a blast making the show and they put in great effort to give us a fantastic product.