On gremlin-dotnet, the GraphSONReader public class and IGraphSONDeserializer public interface uses JToken as a parameter, which is a type defined in the third-party library Newtonsoft's Json.NET.
Even though Json.NET is a well-known library, exposing a third-party library type is usually not a good idea as it tightly couples both libraries, ie: IGraphSONDeserializer implementers will have to use Json.NET.
As we are dealing with JSON data, there is a benefit in parsing once and access the parsed data, like its currently implemented (we should avoid using strings and parse multiple times).
I propose using dynamic instead. In C#, an object of type dynamic is basically a dictionary without compile time checks, which is suitable for scenarios like this one.