In my case I do know some of the Past, Present and Future, but certainly no all of it. I don't even know all my characters, sometimes they simply pop-up. When I write I'm kind of watching a movie that is playing in my head and very quickly trying to turn into words, almost like a waking dream. So I'm still surprised about a lot that happens, even about a lot that's said and done. And sometimes I'm left in a bit of tight spot, not knowing how I should solve something or get out of a certain situation. And that's why I love writing and why I have tones of fun doing it. Yes, it is fundamentally my world since I created it, but it's still surprising and new at every turn. And since I created it, well, I'm bound to like it and have some fun.
Then, regarding the readers, I suppose that there are people to like and enjoying just about everything that exists out there. So it's like paths crossing. A reader that likes the same things that you like stumbles into your story, and bam! You got yourself a fan :)
I think that worrying too much if it's interesting to others is not what's most important. Some people will love the mystery and not knowing right up front what's happening. Some will get annoyed and go like, what the hell, I don't get any of this! The most important thing is that you, as a writer, are having fun with what you're building. Building worlds is a hard process, and you'll probably have to go back, and back again, and rewrite, and re-read. If you don't have enough love for it, you'll probably just end up giving up. You know? When you're in love you can take almost anything from your loved one, and you will still love it even if no one else does. That's what writing is all about. (my humble opinion, of course ^_^;)