I am in somewhat similar position to you, I have solidish GDD ( to be changed a million times during production ) and I invested time in thinking. If you don't have proven track record, I doubt you can create hype just by promoting it. Although Godus doesn't :) , "a new game from Molyneux" sounds promising.

Once again from my experience, people like to give feedback when you ask their opinion, so I'd suggest checking forums of similar games and see what they fail at, also simply ask people.

But there is a problem most times, because people didn't invest the time you did, they most time are having difficulty in giving something valuable. In order to overcome this, I think finding promising people and invite them for contribution to a forum you'll have.

I confess that I misread the thread. I saw the OP express a desire for user input and ask whether he should [do something] to obtain it [or just continue development without it], to which someone else responded, saying just continue development. In my previous responses above, I was reacting to that other person's suggestion -- I overlooked that the OP was looking for what the something ought to be. I'm sorry that my responses were unhelpful to the OP.