What is it that makes a Pokemon a worthwhile addition to the franchise, in your opinion?

There are various threads where people call a Pokemon shit or post their favorites. However, what is it that draws you to a Pokemon or makes you like them?

In the past for me it was almost entirely personal aesthetic appeal. I also kind of tended to favor Pokemon that were animals over inanimate objects or other things.

Lately though I find myself interested in what a Pokemon is based off of. Sometimes Pokemon I've overlooked I find myself liking if they're based on something interesting such as Paras/Parasect. Also for some reason I really like gimmick Pokemon like Chatot, Sawsbuck and Castform. I also tend to favor cute Pokemon.