The speculation TFA invited though is exactly the problem with it. In the two years between movies, it's inevitable that the fans will come up with better ideas than the creators, and thus be disappointed by the lackluster (or outright insulting) reveals.

As the first chapter in the new trilogy, TFA didn't need to throw mysteries in. What it needed was exposition.

The original Star Wars (1977) made this work perfectly. There was no guessing who Luke's dad was, we knew it was Anakin. Then ESB comes along, and turns it on it's head. You weren't expecting a mystery; you weren't expecting a twist. And that's exactly why it works. The audience never even had the chance to guess, and so never had a chance to say it would be predictable, or to think up another alternative. Because they never knew there was a question to begin with.

Episode 7 should have taken the cues from Episode 4 in the ways that matter, not just the superficial ways.