Cool demo, reminds me of Gabriel Knight 1(Interface and graphics) and I loved that game.
My feedback so far:
Pros:
Really great old school adventure, very close to the good old Sierra Adventures(did I mention before that I love these games??)
A very nice story flow( but I'm not so far) I'll update when I'm through the demo.
The graphics are very good drawn, if you did all of them yourself you are very talented!
The interface is good, but to keep the open/close and the use icon, you might think about dropping the open/close and only have the use icon.
But thats only my personal opinion, if you like the open/close then keep it!
The GK Style questioning system is great, I like that very much, I hope that you implement some dialogue puzzles.
Cons:
The sound and the music is not so great, the voice acting is very unclear and I think the music could use some polish.
(if you want, I can help you with the music, you can pm me in german)
In some screens I have a green dot in the left upper corner, not always, but in the Select screen f.e.
What I also do not like is the Ben Jordan sprite for John Sinclair, I think it would have been better to either redraw him completely or use the GK1 Sprite and modify it(I think the GK sprite was the best possible VGA Sprite ever drawn)
And I need your help, I'm already stuck in the kirche:-)
How can I distract the pfarrer and get rid of the beggar?

If you want some more details I can send that via pm.
Keep up the good work.