I like the way Apigee Edge handles the creation and editing of API proxies. The mechanisms they use for tracing traffic through those proxies is clear and understandable to most people who already know how to run a website.
I like the mechanisms that Apigee provides to throttle APIs (SpikeArrest) and respond with the same results to multiple queries for the same information (Caching) when the same response is appropriate.
I think most of the User Interface is as visual as it can be. There are certain aspects of the features that require a few lines of code, but their transaction maps are diagrams. Review collected by and hosted on G2.com.