Apologies if this has been mentioned at all anywhere else, afraid I don't speak German :)
Firstly, the demo is awesome and I really have high hopes for the finished product.
If the demo's dynamics emulate exactly what the finished product will possess then I have a few comments to make about the problem solving. Not so much to do with the problems themselves, but with how they are illustrated to the player.
Basically (and i'm assuming that your project is meant to emulate the Revolution titles) if something has a small magnifying glass, it usually meant in the previous titles that it was interesting and part of the scenery but served no real purpose aside from fleshing out the environment. But in the demo the table uses this small magnifying glass to illustrate what is a key part of entering the locked room upstairs. Also, the barstools have a cog, which in the previous titles always represented something important, something you could interact with in some way that was important, but you can't interact with the barstools at all. Also in the previous titles the 'fingers picking something up' symbol was used for...well...things you could pick up, and the cups above the bar couldn't be, so them being represented as such is a little pointless.
If your intent was to take a step away from the Revolution series and throw off the player to make things more challenging in some way then disregard what I've said, regardless I thought i'd comment on it.
Other than that the game looks very, very promising, can't wait to play it guys :)