GraphQL can be a good format in some situations, but not quite universally. In general, it's shifting the "smarts" to the frontend. It's more like the application can be moved totally to the client. This is not always a good choice.

I compare GraphQL to semantic web technologies (SPARQL), but the idea with semantic web is different and encourages federation. Graphs can be seamlessly queried from several sources. The open world approach of semantic web makes it tolerant to when some data is missing or too much is said about something (AAA principle - Anyone can say Anything about Any topic). Strictness of GraphQL limits such uses. With semweb it's possible to add completely new knowledge to the application. Thus, in a sense, GraphQL is less useful regarding that extreme. (Of course, one can encode RDF in GraphQL, but what is the point?)

As usual: do not blindly go after the hype, check suitability.