A very atmospheric adventure which gives for than a nod to TV shows such as Secret Army. Whilst I enjoyed running this there are a couple of warnings needed.
Playing with a WW2 background has meant though that if not careful the Cthulhu Mythos threats actually seem quite tame compared to the threat of the Nazi occupation. This is not a bad thing per se, but the temptation to increase the Mythos threat or play down the feelings of the unknown in newly occupied Czechoslovakia needs to be avoided. The foreshadowing of facing the Nazis before the Mythos makes this adventure work.
Perhaps a bigger criticism is that this adventure is designed (it seems to me) to be fight heavy - and that would be a mistake also. Having the NPC soldiers all set to be good at fighting (far better than my scholarly investigators) means the true threat is taken down a notch. Then again having PCs know they are outmatched and having to try harder to avoid combat is entertaining.
The only other warning it that my players correctly asked "is this just like the Wolfenstein games" right at that beginning. Errr - yes was the answer but I had to tweak a few bits (especially the recommended way of playing the last two chapters). If your players have not already said "is that a castle full of Nazi's doing experiments to create zombies" you should be fine.
Despite those criticisms this a very different take on Cthulhu and reffing PCs being spies in WW2 was the most fun I have had with Cthulhu for ages! This adventure may need alot of tweaks for many groups but is very well worth it.