I'm not an expert, but what is the difference between a plain old ESB and what we now call an "API Gateway" or "API Manager" (such as Kong or WSO2) in the world of microservices?

I know of some architectures where the API Gateway has a lot of logic put into it... And you have to go through it to reach any of the microservices in the network.

Isn't this a single point of failure and similar to an ESB?