I like the concept of them more than traditional DLC. With DLC you can only download it as long as the service is available. The amiibo is a form of physical media that can transcend the digital distribution in a sense. Basically, a form of the old physical media vs digital debate.
However I do not support, for example, a hard mode being locked behind it. This is a bad form of DLC and amiibo is no exception.
So I like the concept, not a fan how it is abused sometimes however.