This was really well put together and I'm eagerly awaiting the followup. The storytelling was brilliant and the difficulty was about right... I managed to find 4 of the 5 secrets off my own bat.
My one criticism is that the voice acting in the intro, although well-recorded, sounded a little wooden, people reading a script rather than living the parts. I appreciate that's not going to be easy or quick to change but it might be something to watch out for in the future.
Having an outtro video was excellent, though. I wish more people would do that! It's annoying to have this great story build-up and then... just a score with the intrigue left hanging rather than an aftermath or epilogue of any kind. So very well done for that.