I've built a simple GraphQL server in Clojure using the Lacinia (https://github.com/walmartlabs/lacinia) library. It is about as nice as Apollo to be honest, but you would obviously need to know your way around Clojure.

Lacinia tries to be feature complete (as defined by Apollo Server and GraphQL spec), but obviously does not support everything Apollo does (remote schemas and graphql endpoints for example).

I have not tried any GraphQL server libraries in other languages, so I can't speak for people using C#, Java, or some other language.

I think the tooling around GraphQL is quickly approaching a point where it is better to use GraphQL then REST for client facing services. The fact that you can more precisely define your data needs and don't have to fetch the world, or make multiple round trips, is a big win. The contract a GraphQL schema provides both during development and runtime is also nice.