I'm big on Classic Traveller. You all know that. I have (just this day) acquired T5. Expect a longer blog post as I can't read the whole dang thing in one day. But I started and the following post is the result.
I will critique T5 after I read the whole shebang. But it got me going all meta on game design. As the hour is late and I'm beat I will try to be succinct.
A lot of a RPG or setting's success hangs on knowing what questions to ask and answering them. Classic Traveller asked and answered the required amount for an SF setting, in my opinion, in the core LBBs. That's a good design. Leaving out say, starships, for a splat book is a bad design. Leaving out vehicle combat is a gray area. You can't stick everything in your game though so it is defensible.
Trying to answer every question you can think of is commendable, at least for enthusiasm. It isn't always the right decision. A game still has to be accessible. It has to be affordable. Too much chrome or crunch defeats this.
As a game is played more questions will come up, or questions that seemed unimportant initially become a priority. So we have revisions and splat books. The success of these again depends on how good their answers are and how well the designer chose the questions to answer. I'm looking forward to seeing how good T5's questions and answers are.