I think the stdlib is awesome, but the biggest gripe I have with the standard net/http library would be the multiplexer (ServeMux). Out of the box if you provide it with a handle like /foo but the user making a request adds a trailing slash (e.g. GET /foo/), it returns a 404, compared to other libraries like julienschmidt/httprouter which will handle cases like this for you.
For example: https://play.golang.org/p/Q96EulBUfI
Other than that I think the stdlib is bang-on for simple http servers. Wouldn't recommend it if you're planning on writing a web server backed by a database, however. Compared to other web frameworks like django, the stdlib is a great library for working at a lower level in the stack, whereas Django is more of a content-oriented framework built around higher level concepts like basic CRUD applications.
These libraries also support middleware wrapping [1], a technique that the default mux supports but doesn't help you with. For example, adding CORS headers or logging the request.