For the developers it should be easy to learn, it should be stable without lots of changes, backward compatible with no breaking changes from version to version, have very good tooling, have very good package management, have a default way to accomplish things, have batteries included, be easy to debug and deploy.

For users it should be at least fast, responsive, have minimal to no latency, easy to interact with, easy on the eyes, have a coherent design language, be ergonomic, not be a memory or CPU hog.