I really liked Agatha's character. I thought her hamminess was perfect for the sit-com atmosphere, and her eventual reveal (even though everyone knew it was coming) as an opportunistic parasite was great.
However, it seems a stretch to have her own show. I'll probably watch it, but I'm not really sure where they can go with the character, particularly as left at the end of WandaVision. It will interesting to see what they try to do.