Not bad, but fell slightly short
This is a rather long review. Please bear with me, and take what you like from it.
As a puzzler, this was pretty good. The puzzles were clear cut, the solutions were not obscure, and it's good that it never resorted to pixel hunting.
As an adventure game, however, this fell a little short of the expectations it set for itself. The atmosphere hinted at something sinister, from the starting premise to the music to the odd quirks within the building, but the game never cashed in on it. If the story were unimportant, it would probably have been more satisfying with a straightforward storyline, for example a rich but eccentric millionaire dares you to try to escape his newly constructed office building. Something simple, perhaps.
If the story IS important, then at least some sort of teaser should have been thrown in to keep the player interested. Perhaps explain why the papers are blue or why a certain entrance point is so obscurely placed. In fact, why is a key dangling out of reach without any rhyme or reason? If it's some diabolical plan, we'd like to know more.
As daakmore stated below, care should also be taken with the solutions. If a more obvious solution is presented but is not allowed, it only serves to frustrate the player. Try to make sure that the solution you set up is the only (or at least the most plausible) solution available. It is often a thrill for the player if the resolution of a puzzle makes the player go "oh gosh, that's brilliant. Why didn't I think of that earlier?"
As stated before, the ending does not help to cash in on the game's general atmosphere. Without an overarching story and motivation, this game just feels... reduced. Which is a waste, considering the amount of freedom the plot grants you.
All in all, a pretty good puzzler, but if you were aiming for an adventure game, there are some rather unfortunate flaws, but I believe your future efforts would be worth keeping an eye out for.