There is no simple answer and there are many different philosophical stances that people take. For some, a good toy is "green" first and foremost. Some people disdain plastic and prefer toys made of wood. Others do not like toys that are promoted on TV and shop instead in specialty stores for products that are not mass-marketed. I would suggest that kids, of course, don’t care about these things.
Many do not like their children to play with any form of gun, toy weapon, or other "violent" toy. Some do not want their children, their daughters in particular, to play with Barbie-type dolls or pink toys. Other parents may not want their boys to play with dolls and other gentler and more nurturing products.
Many people hated the Garbage Pail Kids and Cabbage Patch Kids, though for somewhat different reasons, but kids loved them. Some parents hate toys that require batteries or leave a mess. But kids love them, as well. What kid doesn’t love slime or Play Doh?
The Germans like dolls with glass eyes, and not the painted eyes common in the US and elsewhere. French mothers historically reject electronic animatronic plush, so popular elsewhere, as "watch me" toys and not sufficiently interactive.
It begs the question, "What is a good toy?" If a toy stands the test of time, then by definition it must be a good toy, of course. But what of others?
Toys are like food. I may not like tofu, but that doesn’t make it bad food, just not to my taste. I am also not a fan of Indian, Vegetarian, or even French cuisine. I favor Scotch over wine. Those are my tastes and not a criticism of the foods for which I do not have a fondness.
If a toy is compelling and kids can’t put it down, but want to play with it again and again, I would argue that is a measure of a good product. Not all toys need to be to everyone's tastes, but a good toy is one that entertains and delights.