It may be helpful to quote the Phase II series bible's description (as reprinted in the Reeves-Stevens' 'Lost Series' book) of Decker, who was of course the inspiration for Riker. The bible describes Decker (p 90) as
And that's pretty much how I've always seen Frakes's portrayal of Riker - an illusion of a one-dimensional person because it's in some ways all in fun to him. It's debatable whether this was purposefully carried over to Riker, but I'm guessing it was. I know some people don't like him, and IDIC, but I do and I think he did a good job....a very humorous man. He particularly enjoys playing the 'too perfect' soulless marionette of an officer. The joke can be confusing to others because Will can become almost that kind of officer when Kirk's welfare or the safety of the ship is involved.